A.18.10 The Generic Package Containers.Multiway_Trees
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The language-defined generic package Containers.Multiway_Trees provides
private types Tree and Cursor, and a set of operations for each type.
A multiway tree container is well-suited to represent nested structures.
Discussion: {
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This tree just provides a basic structure, and make no promises about
balancing or other automatic organization. In this sense, it is different
than the indexed (Map, Set) forms. Rather, it provides a building block
on which to construct more complex and more specialized tree containers.
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A multiway tree container object manages a tree of
nodes, consisting
of a
root node and a set
of
internal nodes; each internal node contains
an element and pointers to the parent, first child, last child, next
(successor) sibling, and previous (predecessor) sibling internal nodes.
A cursor designates a particular node within a tree (and by extension
the element contained in that node, if any). A cursor keeps designating
the same node (and element) as long as the node is part of the container,
even if the node is moved within the container.
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{
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A
subtree is a particular node (which
roots the subtree)
and all of its child nodes (including all of the children of the child
nodes, recursively).
The
root node is always present and has neither an associated element value
nor any parent node; it has pointers to its first child and its last
child, if any. The root node provides a place to add nodes to an otherwise
empty tree and represents the base of the tree.
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A node that has no children is called a
leaf node.
The
ancestors of a node are the node itself, its parent node,
the parent of the parent node, and so on until a node with no parent
is reached.
Similarly, the
descendants of
a node are the node itself, its child nodes, the children of each child
node, and so on.
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{
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The nodes of a subtree can be visited in several different orders. For
a
depth-first order, after visiting a node, the nodes of its child
list are each visited in depth-first order, with each child node visited
in natural order (first child to last child).
Ramification: For the depth-first order,
when each child node is visited, the child list of the child node is
visited before the next sibling of the child node is visited.
Static Semantics
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The generic library package Containers.Multiway_Trees has the following
declaration:
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with Ada.Iterator_Interfaces;
generic
type Element_Type
is private;
with function "=" (Left, Right : Element_Type)
return Boolean
is <>;
package Ada.Containers.Multiway_Trees
with Preelaborate, Remote_Types,
Nonblocking, Global =>
in out synchronized isDiscussion: {
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For discussion on the reasons and meaning of the specifications of the
Global and Nonblocking aspects in this generic package, see the notes
on the equivalent operations in the specification of the Containers.Vectors
package (see
A.18.2).
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{
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{
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{
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{
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type Tree
is tagged private
with Constant_Indexing => Constant_Reference,
Variable_Indexing => Reference,
Default_Iterator => Iterate,
Iterator_Element => Element_Type,
Iterator_View => Stable.Tree,
Stable_Properties => (Node_Count,
Tampering_With_Cursors_Prohibited,
Tampering_With_Elements_Prohibited),
Default_Initial_Condition =>
Node_Count (Tree) = 1
and then
(
not Tampering_With_Cursors_Prohibited (Tree))
and then
(
not Tampering_With_Elements_Prohibited (Tree)),
Preelaborable_Initialization;
{
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type Cursor
is private
with Preelaborable_Initialization;
Empty_Tree :
constant Tree;
No_Element :
constant Cursor;
{
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function Equal_Element (Left, Right : Element_Type)
return Boolean
renames "=";
{
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{
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function Has_Element (Position : Cursor)
return Boolean
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
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function Has_Element (Container : Tree; Position : Cursor)
return Boolean
with Nonblocking, Global =>
null, Use_Formal =>
null;
{
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package Tree_Iterator_Interfaces
is new
Ada.Iterator_Interfaces (Cursor, Has_Element);
function Equal_Subtree (Left_Position : Cursor;
Right_Position: Cursor)
return Boolean;
function "=" (Left, Right : Tree) return Boolean;
{
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function Tampering_With_Cursors_Prohibited
(Container : Tree)
return Boolean
with Nonblocking, Global =>
null, Use_Formal =>
null;
{
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function Tampering_With_Elements_Prohibited
(Container : Tree)
return Boolean
with Nonblocking, Global =>
null, Use_Formal =>
null;
{
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function Empty
return Tree
is (Empty_Tree)
with Post =>
not Tampering_With_Elements_Prohibited (Empty'Result)
and then
not Tampering_With_Cursors_Prohibited (Empty'Result)
and then
Node_Count (Empty'Result) = 1;
{
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function Is_Empty (Container : Tree)
return Boolean
with Nonblocking, Global =>
null, Use_Formal =>
null,
Post => Is_Empty'Result = (Node_Count (Container) = 1);
{
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function Node_Count (Container : Tree)
return Count_Type
with Nonblocking, Global =>
null, Use_Formal =>
null;
{
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function Subtree_Node_Count (Position : Cursor)
return Count_Type
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
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function Subtree_Node_Count (Container : Tree; Position : Cursor)
return Count_Type
with Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Nonblocking, Global =>
null, Use_Formal =>
null;
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function Depth (Position : Cursor)
return Count_Type
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
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function Depth (Container : Tree; Position : Cursor)
return Count_Type
with Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Nonblocking, Global =>
null, Use_Formal =>
null;
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function Is_Root (Position : Cursor)
return Boolean
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
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function Is_Root (Container : Tree; Position : Cursor)
return Boolean
with Nonblocking, Global =>
null, Use_Formal =>
null;
{
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function Is_Leaf (Position : Cursor)
return Boolean
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
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function Is_Leaf (Container : Tree; Position : Cursor)
return Boolean
with Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Nonblocking, Global =>
null, Use_Formal =>
null;
{
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function Is_Ancestor_Of (Container : Tree;
Parent : Cursor;
Position : Cursor)
return Boolean
with Pre => (Meaningful_For (Container, Position)
or else raise Program_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error),
Nonblocking, Global =>
null, Use_Formal =>
null;
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function Root (Container : Tree)
return Cursor
with Nonblocking, Global =>
null, Use_Formal =>
null,
Post => Root'Result /= No_Element
and then
not Has_Element (Container, Root'Result);
{
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function Meaningful_For (Container : Tree; Position : Cursor)
return Boolean
is
(Position = No_Element
or else
Is_Root (Container, Position)
or else
Has_Element (Container, Position))
with Nonblocking, Global =>
null, Use_Formal =>
null;
Reason: {
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When this function is true, the Position can be meaningfully used with
operations for Container. We define this because many operations allow
the root (which does not have an element, so Has_Element returns False),
so many preconditions get unwieldy. We allow No_Element as it is allowed
by many queries, and for existing routines, it raises a different exception
(Constraint_Error rather than Program_Error) than a cursor for the wrong
container does.
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procedure Clear (Container :
in out Tree)
with Pre =>
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error,
Post => Node_Count (Container) = 1;
{
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function Element (Position : Cursor)
return Element_Type
with Pre => (Position /= No_Element
or else
raise Constraint_Error)
and then
(Has_Element (Position)
or else raise Program_Error),
Nonblocking, Global =>
in all, Use_Formal => Element_Type;
{
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function Element (Container : Tree;
Position : Cursor)
return Element_Type
with Pre => (Position /= No_Element
or else
raise Constraint_Error)
and then
(Has_Element (Container, Position)
or else raise Program_Error),
Nonblocking, Global =>
null, Use_Formal => Element_Type;
{
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procedure Replace_Element (Container :
in out Tree;
Position :
in Cursor;
New_item :
in Element_Type)
with Pre => (
not Tampering_With_Elements_Prohibited (Container)
or else raise Program_Error)
and then
(Position /= No_Element
or else raise Constraint_Error)
and then
(Has_Element (Container, Position)
or else raise Program_Error);
{
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procedure Query_Element
(Position :
in Cursor;
Process :
not null access procedure (Element :
in Element_Type))
with Pre => (Position /= No_Element
or else raise Constraint_Error)
and then
(Has_Element (Position)
or else raise Program_Error),
Global =>
in all;
{
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procedure Query_Element
(Container :
in Tree;
Position :
in Cursor;
Process :
not null access procedure (Element :
in Element_Type))
with Pre => (Position /= No_Element
or else raise Constraint_Error)
and then
(Has_Element (Container, Position)
or else raise Program_Error);
{
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procedure Update_Element
(Container :
in out Tree;
Position :
in Cursor;
Process :
not null access procedure
(Element :
in out Element_Type))
with Pre => (Position /= No_Element
or else raise Constraint_Error)
and then
(Has_Element (Container, Position)
or else raise Program_Error);
{
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{
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type Constant_Reference_Type
(Element :
not null access constant Element_Type)
is private
with Implicit_Dereference => Element,
Nonblocking, Global =>
in out synchronized,
Default_Initial_Condition => (
raise Program_Error);
{
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{
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type Reference_Type (Element :
not null access Element_Type)
is private
with Implicit_Dereference => Element,
Nonblocking, Global =>
in out synchronized,
Default_Initial_Condition => (
raise Program_Error);
{
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{
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function Constant_Reference (Container :
aliased in Tree;
Position :
in Cursor)
return Constant_Reference_Type
with Pre => (Position /= No_Element
or else raise Constraint_Error)
and then
(Has_Element (Container, Position)
or else raise Program_Error),
Post => Tampering_With_Cursors_Prohibited (Container),
Nonblocking, Global =>
null, Use_Formal =>
null;
{
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{
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function Reference (Container :
aliased in out Tree;
Position :
in Cursor)
return Reference_Type
with Pre => (Position /= No_Element
or else raise Constraint_Error)
and then
(Has_Element (Container, Position)
or else raise Program_Error),
Post => Tampering_With_Cursors_Prohibited (Container),
Nonblocking, Global =>
null, Use_Formal =>
null;
{
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procedure Assign (Target :
in out Tree; Source :
in Tree)
with Pre =>
not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error,
Post => Node_Count (Source) = Node_Count (Target);
{
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function Copy (Source : Tree)
return Tree
with Post =>
Node_Count (Copy'Result) = Node_Count (Source)
and then
not Tampering_With_Elements_Prohibited (Copy'Result)
and then
not Tampering_With_Cursors_Prohibited (Copy'Result);
{
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procedure Move (Target :
in out Tree;
Source :
in out Tree)
with Pre => (
not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error)
and then
(
not Tampering_With_Cursors_Prohibited (Source)
or else raise Program_Error),
Post => (
if not Target'Has_Same_Storage (Source)
then
Node_Count (Target) = Node_Count (Source'Old)
and then
Node_Count (Source) = 1);
{
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procedure Delete_Leaf (Container :
in out Tree;
Position :
in out Cursor)
with Pre => (
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error)
and then
(Position /= No_Element
or else raise Constraint_Error)
and then
(Has_Element (Container, Position)
or else raise Program_Error)
and then
(Is_Leaf (Container, Position)
or else raise Constraint_Error),
Post =>
Node_Count (Container)'Old = Node_Count (Container)+1
and then
Position = No_Element;
{
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procedure Delete_Subtree (Container :
in out Tree;
Position :
in out Cursor)
with Pre => (
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error)
and then
(Position /= No_Element
or else raise Constraint_Error)
and then
(Has_Element (Container, Position)
or else raise Program_Error),
Post => Node_Count (Container)'Old = Node_Count (Container) +
Subtree_Node_Count (Container, Position)'Old
and then
Position = No_Element;
{
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procedure Swap (Container :
in out Tree;
I, J :
in Cursor)
with Pre => (
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error)
and then
(I /= No_Element
or else Constraint_Error)
and then
(J /= No_Element
or else Constraint_Error)
and then
(Has_Element (Container, I)
or else raise Program_Error)
and then
(Has_Element (Container, J)
or else raise Program_Error);
{
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function Find (Container : Tree;
Item : Element_Type)
return Cursor
with Post => (
if Find'Result /= No_Element
then Has_Element (Container, Find'Result));
{
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{
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{
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function Find_In_Subtree (Position : Cursor;
Item : Element_Type)
return Cursor
with Pre => Position /= No_Element
or else raise Constraint_Error,
Post => (
if Find_In_Subtree'Result = No_Element
then Has_Element (Find_In_Subtree'Result)),
Global =>
in all;
{
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function Find_In_Subtree (Container : Tree;
Position : Cursor;
Item : Element_Type)
return Cursor
with Pre => (Position /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Position)
or else raise Program_Error),
Post => (
if Find_In_Subtree'Result /= No_Element
then Has_Element (Container, Find_In_Subtree'Result));
{
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{
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{
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function Ancestor_Find (Position : Cursor;
Item : Element_Type)
return Cursor
with Pre => Position /= No_Element
or else raise Constraint_Error,
Post => (
if Ancestor_Find'Result = No_Element
then Has_Element (Ancestor_Find'Result)),
Global =>
in all;
{
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function Ancestor_Find (Container : Tree;
Position : Cursor;
Item : Element_Type)
return Cursor
with Pre => (Position /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Position)
or else raise Program_Error),
Post => (
if Ancestor_Find'Result = No_Element
then Has_Element (Container, Ancestor_Find'Result));
function Contains (Container : Tree;
Item : Element_Type)
return Boolean;
{
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procedure Iterate
(Container :
in Tree;
Process :
not null access procedure (Position :
in Cursor))
with Allows_Exit;
{
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procedure Iterate_Subtree
(Position :
in Cursor;
Process :
not null access procedure (Position :
in Cursor))
with Allows_Exit,
Pre => Position /= No_Element
or else raise Constraint_Error,
Global =>
in all;
{
AI12-0112-1}
procedure Iterate_Subtree
(Container :
in Tree;
Position :
in Cursor;
Process :
not null access procedure (Position :
in Cursor))
with Allows_Exit,
Pre => (Position /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Position)
or else raise Program_Error);
{
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{
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{
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function Iterate (Container :
in Tree)
return Tree_Iterator_Interfaces.Parallel_Iterator'Class
with Post => Tampering_With_Cursors_Prohibited (Container);
{
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{
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{
AI12-0266-1}
function Iterate_Subtree (Position :
in Cursor)
return Tree_Iterator_Interfaces.Parallel_Iterator'Class
with Pre => Position /= No_Element
or else raise Constraint_Error,
Global =>
in all;
{
AI12-0112-1}
function Iterate_Subtree (Container :
in Tree; Position :
in Cursor)
return Tree_Iterator_Interfaces.Parallel_Iterator'Class
with Pre => (Position /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Position)
or else raise Program_Error),
Post => Tampering_With_Cursors_Prohibited (Container);
{
AI12-0112-1}
function Child_Count (Parent : Cursor)
return Count_Type
with Post => (
if Parent = No_Element
then Child_Count'Result = 0),
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
AI12-0112-1}
function Child_Count (Container : Tree; Parent : Cursor)
return Count_Type
with Pre => Meaningful_For (Container, Parent)
or else raise Program_Error,
Post => (
if Parent = No_Element
then Child_Count'Result = 0),
Nonblocking, Global =>
null, Use_Formal =>
null;
{
AI12-0112-1}
function Child_Depth (Parent, Child : Cursor)
return Count_Type
with Pre => (Parent = No_Element
and then Child = No_Element)
or else raise Constraint_Error,
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
AI12-0112-1}
function Child_Depth (Container : Tree; Parent, Child : Cursor)
return Count_Type
with Pre => ((Parent = No_Element
and then Child = No_Element)
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error)
and then
(Meaningful_For (Container, Child)
or else raise Program_Error),
Nonblocking, Global =>
null, Use_Formal =>
null;
{
AI12-0112-1}
procedure Insert_Child (Container :
in out Tree;
Parent :
in Cursor;
Before :
in Cursor;
New_Item :
in Element_Type;
Count :
in Count_Type := 1)
with Pre => (
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error)
and then
(Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error)
and then
(Meaningful_For (Container, Before)
or else raise Program_Error)
and then
(Before = No_Element
or else
Container.Parent (Before) = Parent
or else raise Constraint_Error),
Post => Node_Count (Container) =
Node_Count (Container)'Old + Count;
{
AI12-0112-1}
procedure Insert_Child (Container :
in out Tree;
Parent :
in Cursor;
Before :
in Cursor;
New_Item :
in Element_Type;
Position :
out Cursor;
Count :
in Count_Type := 1)
with Pre => (
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error)
and then
(Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error)
and then
(Meaningful_For (Container, Before)
or else raise Program_Error)
and then
(Before = No_Element
or else
Container.Parent (Before) = Parent
or else raise Constraint_Error),
Post => (Node_Count (Container) =
Node_Count (Container)'Old + Count)
and then
Has_Element (Container, Position);
{
AI12-0112-1}
procedure Insert_Child (Container :
in out Tree;
Parent :
in Cursor;
Before :
in Cursor;
Position :
out Cursor;
Count :
in Count_Type := 1)
with Pre => (
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error)
and then
(Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error)
and then
(Meaningful_For (Container, Before)
or else raise Program_Error)
and then
(Before = No_Element
or else
Container.Parent (Before) = Parent
or else raise Constraint_Error),
Post => (Node_Count (Container) =
Node_Count (Container)'Old + Count)
and then
Has_Element (Container, Position);
{
AI12-0112-1}
procedure Prepend_Child (Container :
in out Tree;
Parent :
in Cursor;
New_Item :
in Element_Type;
Count :
in Count_Type := 1)
with Pre => (
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error)
and then
(Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error),
Post => Node_Count (Container) =
Node_Count (Container)'Old + Count;
{
AI12-0112-1}
procedure Append_Child (Container :
in out Tree;
Parent :
in Cursor;
New_Item :
in Element_Type;
Count :
in Count_Type := 1)
with Pre => (
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error)
and then
(Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error),
Post => Node_Count (Container) =
Node_Count (Container)'Old + Count;
{
AI12-0112-1}
procedure Delete_Children (Container :
in out Tree;
Parent :
in Cursor)
with Pre => (
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error)
and then
(Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error),
Post => (Node_Count (Container) = Node_Count (Container)'Old -
Child_Count (Container, Parent)'Old)
and then
Child_Count (Container, Parent) = 0;
{
AI12-0112-1}
procedure Copy_Subtree (Target :
in out Tree;
Parent :
in Cursor;
Before :
in Cursor;
Source :
in Cursor)
with Pre => (
not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error)
and then
(Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Target, Parent)
or else raise Program_Error)
and then
(Meaningful_For (Target, Before)
or else raise Program_Error)
and then
(Before = No_Element
or else
Target.Parent (Before) = Parent
or else raise Constraint_Error)
and then
(
not Is_Root (Source)
or else raise Constraint_Error),
Post => Node_Count (Target) =
Node_Count (Target)'Old + Subtree_Node_Count (Source),
Global =>
in all;
{
AI12-0112-1}
procedure Copy_Local_Subtree (Target :
in out Tree;
Parent :
in Cursor;
Before :
in Cursor;
Source :
in Cursor)
with Pre => (
not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error)
and then
(Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Target, Parent)
or else raise Program_Error)
and then
(Meaningful_For (Target, Before)
or else raise Program_Error)
and then
(Before = No_Element
or else
Target.Parent (Before) = Parent
or else raise Constraint_Error)
and then
(Meaningful_For (Target, Source)
or else raise Program_Error)
and then
(
not Is_Root (Source)
or else raise Constraint_Error),
Post => Node_Count (Target) = Node_Count (Target)'Old +
Subtree_Node_Count (Target, Source);
{
AI12-0112-1}
procedure Copy_Subtree (Target :
in out Tree;
Parent :
in Cursor;
Before :
in Cursor;
Source :
in Tree;
Subtree :
in Cursor)
with Pre => (
not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error)
and then
(Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Target, Parent)
or else raise Program_Error)
and then
(Meaningful_For (Target, Before)
or else raise Program_Error)
and then
(Before = No_Element
or else
Target.Parent (Before) = Parent
or else raise Constraint_Error)
and then
(Meaningful_For (Source, Subtree)
or else raise Program_Error)
and then
(
not Is_Root (Source, Subtree)
or else raise Constraint_Error),
Post => Node_Count (Target) = Node_Count (Target)'Old +
Subtree_Node_Count (Source, Subtree);
{
AI12-0112-1}
procedure Splice_Subtree (Target :
in out Tree;
Parent :
in Cursor;
Before :
in Cursor;
Source :
in out Tree;
Position :
in out Cursor)
with Pre => (
not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error)
and then
(
not Tampering_With_Cursors_Prohibited (Source)
or else raise Program_Error)
and then
(Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Target, Parent)
or else raise Program_Error)
and then
(Meaningful_For (Target, Before)
or else raise Program_Error)
and then
(Before = No_Element
or else
Target.Parent (Before) /= Parent
or else raise Constraint_Error)
and then
(Position /= No_Element
or else raise Constraint_Error)
and then
(Has_Element (Source, Position)
or else raise Program_Error)
and then
(Target'Has_Same_Storage (Source)
or else
Position = Before
or else
Is_Ancestor_Of (Target, Position, Parent)
or else raise Constraint_Error),
Post => (
declare
Org_Sub_Count
renames
Subtree_Node_Count (Source, Position)'Old;
Org_Target_Count
renames Node_Count (Target)'Old;
begin
(
if not Target'Has_Same_Storage (Source)
then
Node_Count (Target) = Org_Target_Count +
Org_Sub_Count
and then
Node_Count (Source) = Node_Count (Source)'Old -
Org_Sub_Count
and then
Has_Element (Target, Position)
else
Target.Parent (Position) = Parent
and then
Node_Count (Target) = Org_Target_Count));
{
AI12-0112-1}
procedure Splice_Subtree (Container:
in out Tree;
Parent :
in Cursor;
Before :
in Cursor;
Position :
in Cursor)
with Pre => (
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error)
and then
(Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error)
and then
(Meaningful_For (Container, Before)
or else raise Program_Error)
and then
(Before = No_Element
or else
Container.Parent (Before) /= Parent
or else raise Constraint_Error)
and then
(Position /= No_Element
or else raise Constraint_Error)
and then
(Has_Element (Container, Position)
or else raise Program_Error)
and then
(Position = Before
or else
Is_Ancestor_Of (Container, Position, Parent)
or else raise Constraint_Error),
Post => (Node_Count (Container) =
Node_Count (Container)'Old
and then
Container.Parent (Position) = Parent);
{
AI12-0112-1}
procedure Splice_Children (Target :
in out Tree;
Target_Parent :
in Cursor;
Before :
in Cursor;
Source :
in out Tree;
Source_Parent :
in Cursor)
with Pre => (
not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error)
and then
(
not Tampering_With_Cursors_Prohibited (Source)
or else raise Program_Error)
and then
(Target_Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Target, Target_Parent)
or else raise Program_Error)
and then
(Meaningful_For (Target, Before)
or else raise Program_Error)
and then
(Source_Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Source, Source_Parent)
or else raise Program_Error)
and then
(Before = No_Element
or else
Parent (Target, Before) /= Target_Parent
or else raise Constraint_Error)
and then
(Target'Has_Same_Storage (Source)
or else
Target_Parent = Source_Parent
or else
Is_Ancestor_Of (Target, Source_Parent, Target_Parent)
or else raise Constraint_Error),
Post => (
declare
Org_Child_Count
renames
Child_Count (Source, Source_Parent)'Old;
Org_Target_Count
renames Node_Count (Target)'Old;
begin
(
if not Target'Has_Same_Storage (Source)
then
Node_Count (Target) = Org_Target_Count +
Org_Child_Count
and then
Node_Count (Source) = Node_Count (Source)'Old -
Org_Child_Count
else
Node_Count (Target) = Org_Target_Count));
{
AI12-0112-1}
procedure Splice_Children (Container :
in out Tree;
Target_Parent :
in Cursor;
Before :
in Cursor;
Source_Parent :
in Cursor)
with Pre => (
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error)
and then
(Target_Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Target_Parent)
or else raise Program_Error)
and then
(Meaningful_For (Container, Before)
or else raise Program_Error)
and then
(Source_Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Source_Parent)
or else raise Program_Error)
and then
(Before = No_Element
or else
Parent (Container, Before) /= Target_Parent
or else raise Constraint_Error)
and then
(Target_Parent = Source_Parent
or else
Is_Ancestor_Of (Container, Source_Parent, Target_Parent)
or else raise Constraint_Error),
Post => Node_Count (Container) = Node_Count (Container)'Old;
{
AI12-0112-1}
function Parent (Position : Cursor)
return Cursor
with Nonblocking, Global =>
in all, Use_Formal =>
null,
Post => (
if Position = No_Element
or else
Is_Root (Position)
then Parent'Result = No_Element);
{
AI12-0112-1}
function Parent (Container : Tree;
Position : Cursor)
return Cursor
with Nonblocking, Global =>
null, Use_Formal =>
null,
Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Post => (
if Position = No_Element
or else
Is_Root (Container, Position)
then Parent'Result = No_Element
else Has_Element (Container, Parent'Result));
{
AI12-0112-1}
function First_Child (Parent : Cursor)
return Cursor
with Nonblocking, Global =>
in all, Use_Formal =>
null,
Pre => Parent /= No_Element
or else raise Constraint_Error;
{
AI12-0112-1}
function First_Child (Container : Tree;
Parent : Cursor)
return Cursor
with Nonblocking, Global =>
null, Use_Formal =>
null,
Pre => (Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error),
Post => First_Child'Result = No_Element
or else
Has_Element (Container, First_Child'Result);
{
AI12-0112-1}
function First_Child_Element (Parent : Cursor)
return Element_Type
with Nonblocking, Global =>
in all, Use_Formal => Element_Type,
Pre => (Parent /= No_Element
and then
Last_Child (Parent) /= No_Element)
or else raise Constraint_Error;
{
AI12-0112-1}
function First_Child_Element (Container : Tree;
Parent : Cursor)
return Element_Type
with Nonblocking, Global =>
null, Use_Formal => Element_Type,
Pre => (Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error)
and then
(First_Child (Container, Parent) /= No_Element
or else raise Constraint_Error);
{
AI12-0112-1}
function Last_Child (Parent : Cursor)
return Cursor
with Nonblocking, Global =>
in all, Use_Formal =>
null,
Pre => Parent /= No_Element
or else raise Constraint_Error;
{
AI12-0112-1}
function Last_Child (Container : Tree;
Parent : Cursor)
return Cursor
with Nonblocking, Global =>
null, Use_Formal =>
null,
Pre => (Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error),
Post => Last_Child'Result = No_Element
or else
Has_Element (Container, Last_Child'Result);
{
AI12-0112-1}
function Last_Child_Element (Parent : Cursor)
return Element_Type
with Nonblocking, Global =>
in all, Use_Formal => Element_Type,
Pre => (Parent /= No_Element
and then
Last_Child (Parent) /= No_Element)
or else raise Constraint_Error;
{
AI12-0112-1}
function Last_Child_Element (Container : Tree;
Parent : Cursor)
return Element_Type
with Nonblocking, Global =>
null, Use_Formal => Element_Type,
Pre => (Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error)
and then
(Last_Child (Container, Parent) /= No_Element
or else raise Constraint_Error);
{
AI12-0112-1}
function Next_Sibling (Position : Cursor)
return Cursor
with Nonblocking, Global =>
in all, Use_Formal =>
null,
Post => (
if Position = No_Element
then Next_Sibling'Result = No_Element);
{
AI12-0112-1}
function Next_Sibling (Container : Tree;
Position : Cursor)
return Cursor
with Nonblocking, Global =>
null, Use_Formal =>
null,
Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Post => (
if Next_Sibling'Result = No_Element
then
Position = No_Element
or else
Is_Root (Container, Position)
or else
Last_Child (Container, Parent (Container, Position))
= Position
else Has_Element (Container, Next_Sibling'Result));
{
AI12-0112-1}
procedure Next_Sibling (Position :
in out Cursor)
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
AI12-0112-1}
procedure Next_Sibling (Container :
in Tree;
Position :
in out Cursor)
with Nonblocking, Global =>
null, Use_Formal =>
null,
Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Post => (
if Position /= No_Element
then Has_Element (Container, Position));
{
AI12-0112-1}
function Previous_Sibling (Position : Cursor)
return Cursor
with Nonblocking, Global =>
in all, Use_Formal =>
null,
Post => (
if Position = No_Element
then Previous_Sibling'Result = No_Element);
{
AI12-0112-1}
function Previous_Sibling (Container : Tree;
Position : Cursor)
return Cursor
with Nonblocking, Global =>
null, Use_Formal =>
null,
Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Post => (
if Previous_Sibling'Result = No_Element
then
Position = No_Element
or else
Is_Root (Container, Position)
or else
First_Child (Container, Parent (Container, Position))
= Position
else Has_Element (Container, Previous_Sibling'Result));
{
AI12-0112-1}
procedure Previous_Sibling (Position :
in out Cursor)
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
AI12-0112-1}
procedure Previous_Sibling (Container :
in Tree;
Position :
in out Cursor)
with Nonblocking, Global =>
null, Use_Formal =>
null,
Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Post => (
if Position /= No_Element
then Has_Element (Container, Position));
{
AI05-0136-1}
{
AI05-0248-1}
{
AI12-0112-1}
procedure Iterate_Children
(Parent :
in Cursor;
Process :
not null access procedure (Position :
in Cursor))
with Allows_Exit,
Pre => Parent /= No_Element
or else raise Constraint_Error,
Global =>
in all, Use_Formal =>
null;
{
AI12-0112-1}
procedure Iterate_Children
(Container :
in Tree;
Parent :
in Cursor;
Process :
not null access procedure (Position :
in Cursor))
with Allows_Exit,
Pre => (Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error);
{
AI05-0136-1}
{
AI05-0248-1}
{
AI12-0112-1}
procedure Reverse_Iterate_Children
(Parent :
in Cursor;
Process :
not null access procedure (Position :
in Cursor))
with Allows_Exit,
Pre => Parent /= No_Element
or else raise Constraint_Error,
Global =>
in all, Use_Formal =>
null;
{
AI12-0112-1}
procedure Reverse_Iterate_Children
(Container :
in Tree;
Parent :
in Cursor;
Process :
not null access procedure (Position :
in Cursor))
with Allows_Exit,
Pre => (Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error);
{
AI05-0212-1}
{
AI12-0112-1}
{
AI12-0266-1}
function Iterate_Children (Container :
in Tree; Parent :
in Cursor)
return Tree_Iterator_Interfaces.Parallel_Reversible_Iterator'Class
with Pre => (Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error),
Post => Tampering_With_Cursors_Prohibited (Container);
{
AI12-0111-1}
{
AI12-0399-1}
type Tree (Base :
not null access Multiway_Trees.Tree)
is
tagged limited private
with Constant_Indexing => Constant_Reference,
Variable_Indexing => Reference,
Default_Iterator => Iterate,
Iterator_Element => Element_Type,
Stable_Properties => (Node_Count),
Global =>
null,
Default_Initial_Condition => Node_Count (Tree) = 1,
Preelaborable_Initialization;
{
AI12-0111-1}
function Has_Element (Position : Cursor)
return Boolean
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
AI12-0111-1}
package Tree_Iterator_Interfaces
is new
Ada.Iterator_Interfaces (Cursor, Has_Element);
{
AI12-0111-1}
procedure Assign (Target :
in out Multiway_Trees.Tree;
Source :
in Tree)
with Post => Node_Count (Source) = Node_Count (Target);
{
AI12-0111-1}
function Copy (Source : Multiway_Trees.Tree)
return Tree
with Post => Node_Count (Copy'Result) = Node_Count (Source);
{
AI12-0111-1}
type Constant_Reference_Type
(Element :
not null access constant Element_Type)
is private
with Implicit_Dereference => Element,
Nonblocking, Global =>
null,
Default_Initial_Condition => (
raise Program_Error);
{
AI12-0111-1}
type Reference_Type
(Element :
not null access Element_Type)
is private
with Implicit_Dereference => Element,
Nonblocking, Global =>
null,
Default_Initial_Condition => (
raise Program_Error);
{
AI12-0111-1}
--
Additional subprograms as described in the text
--
are declared here.private
... -- not specified by the language
end Ada.Containers.Multiway_Trees;
{
AI05-0136-1}
The actual function for the generic formal function "=" on
Element_Type values is expected to define a reflexive and symmetric relationship
and return the same result value each time it is called with a particular
pair of values. If it behaves in some other manner, the functions Find,
Reverse_Find, Equal_Subtree, and "=" on tree values return
an unspecified value. The exact arguments and number of calls of this
generic formal function by the functions Find, Reverse_Find, Equal_Subtree,
and "=" on tree values are unspecified.
{
AI05-0136-1}
The type Tree is used to represent trees. The type Tree needs finalization
(see
7.6).
{
AI05-0136-1}
{
AI05-0248-1}
Empty_Tree represents the empty Tree object. It contains only the root
node (Node_Count (Empty_Tree) returns 1). If an object of type Tree is
not otherwise initialized, it is initialized to the same value as Empty_Tree.
{
AI05-0136-1}
No_Element represents a cursor that designates no element. If an object
of type Cursor is not otherwise initialized, it is initialized to the
same value as No_Element.
{
AI05-0136-1}
{
AI12-0434-1}
The primitive "=" operator for type Cursor returns True if
both cursors are No_Element, or designate the same element in the same
container.
To be honest: {
AI12-0434-1}
“The primitive "=" operator” is the one with two
parameters of type Cursor which returns Boolean. We're not talking about
some other (hidden) primitive function named "=".
{
AI05-0136-1}
Execution of the default implementation of the Input, Output, Read, or
Write attribute of type Cursor raises Program_Error.
{
AI05-0136-1}
{
AI05-0248-1}
{
AI05-0262-1}
Tree'Read reads the representation of a tree from the stream, and assigns
to
Item a tree with the same elements and structure as was written
by Tree'Write.
Ramification: Streaming more elements
than the container holds is wrong. For implementation implications of
this rule, see the Implementation Note in
A.18.2.
{
AI05-0136-1}
{
AI12-0111-1}
{
AI12-0112-1}
[Some operations
check for “tampering
with cursors” of a container because they depend on the set of
elements of the container remaining constant, and others check for “tampering
with elements” of a container because they depend on elements of
the container not being replaced.] When tampering with cursors is
prohibited
for a particular tree object
T, Program_Error
is propagated by the finalization of
T[, as well as by a call
that passes
T to certain of the operations of this package, as
indicated by the precondition of such an operation]. Similarly, when
tampering with elements is
prohibited for
T, Program_Error
is propagated by a call that passes
T to certain of the other
operations of this package, as indicated by the precondition of such
an operation.
Paragraphs 81 through
90 are removed as preconditions now describe these rules.
Ramification: We don't need to explicitly
mention
assignment_statement,
because that finalizes the target object as part of the operation, and
finalization of an object is already defined as tampering with cursors.
{
AI12-0112-1}
function Has_Element (Position : Cursor)
return Boolean
with Nonblocking, Global =>
in all, Use_Formal =>
null;
Returns True if
Position designates an element, and returns False otherwise. [In particular,
Has_Element returns False if the cursor designates a root node or equals
No_Element.]
To be honest: {
AI05-0005-1}
{
AI05-0136-1}
This function might not detect cursors that designate deleted elements;
such cursors are invalid (see below) and the result of calling Has_Element
with an invalid cursor is unspecified (but not erroneous).
function Has_Element (Container : Tree; Position : Cursor)
return Boolean
with Nonblocking, Global =>
null, Use_Formal =>
null;
{
AI12-0112-1}
Returns True if Position designates an element in Container, and returns
False otherwise. [In particular, Has_Element returns False if the cursor
designates a root node or equals No_Element.]
function Equal_Subtree (Left_Position : Cursor;
Right_Position: Cursor) return Boolean;
{
AI05-0136-1}
{
AI05-0248-1}
{
AI05-0262-1}
{
AI05-0264-1}
If Left_Position or Right_Position equals No_Element, propagates Constraint_Error.
If the number of child nodes of the element designated by Left_Position
is different from the number of child nodes of the element designated
by Right_Position, the function returns False. If Left_Position designates
a root node and Right_Position does not, the function returns False.
If Right_Position designates a root node and Left_Position does not,
the function returns False. Unless both cursors designate a root node,
the elements are compared using the generic formal equality operator.
If the result of the element comparison is False, the function returns
False. Otherwise, it calls Equal_Subtree on a cursor designating each
child element of the element designated by Left_Position and a cursor
designating the corresponding child element of the element designated
by Right_Position. If any such call returns False, the function returns
False; otherwise, it returns True. Any exception raised during the evaluation
of element equality is propagated.
Ramification: Left_Position and Right_Position
do not need to be from the same tree.
Implementation Note: This wording describes
the canonical semantics. However, the order and number of calls on the
formal equality function is unspecified for all of the operations that
use it in this package, so an implementation can call it as many or as
few times as it needs to get the correct answer. Similarly, a global
rule (see the introduction of
Annex A) says that
language-defined routines are not affected by overriding of other language-defined
routines. This means that no reasonable program can tell how many times
Equal_Subtree is called, and thus an implementation can call it as many
or as few times as it needs to get the correct answer. Specifically,
there is no requirement to call the formal equality or Equal_Subtree
additional times once the answer has been determined.
function "=" (Left, Right : Tree) return Boolean;
{
AI05-0136-1}
{
AI05-0262-1}
If Left and Right denote the same tree object, then the function returns
True. Otherwise, it calls Equal_Subtree with cursors designating the
root nodes of Left and Right; the result is returned. Any exception raised
during the evaluation of Equal_Subtree is propagated.
Implementation Note: Similar considerations
apply here as apply to Equal_Subtree. The actual number of calls performed
is unspecified.
function Tampering_With_Cursors_Prohibited
(Container : Tree) return Boolean
with Nonblocking, Global => null, Use_Formal => null;
{
AI12-0112-1}
Returns True if tampering with cursors or tampering with elements is
currently prohibited for Container, and returns False otherwise.
Reason: {
AI12-0112-1}
Prohibiting tampering with elements also needs to prohibit tampering
with cursors, as deleting an element is similar to replacing it.
Implementation Note: {
AI12-0112-1}
Various contracts elsewhere in this specification require that this function
be implemented with synchronized data. Moreover, it is possible for tampering
to be prohibited by multiple operations (sequentially or in parallel).
Therefore, tampering needs to be implemented with an atomic or protected
counter. The counter is initialized to zero, and is incremented when
tampering is prohibited, and decremented when leaving an area that prohibited
tampering. Function Tampering_With_Cursors_Prohibited returns True if
the counter is nonzero. (Note that any case where the result is not well-defined
for one task is incorrect use of shared variables and would be erroneous
by the rules of
9.10, so no special protection
is needed to read the counter.)
function Tampering_With_Elements_Prohibited
(Container : Tree) return Boolean
with Nonblocking, Global => null, Use_Formal => null;
{
AI12-0112-1}
Always returns False[, regardless of whether tampering with elements
is prohibited].
Reason: {
AI12-0111-1}
A definite element cannot change size, so we allow operations that tamper
with elements even when tampering with elements is prohibited. That's
not true for the indefinite containers, which is why this kind of tampering
exists.
function Is_Empty (Container : Tree) return Boolean
with Nonblocking, Global => null, Use_Formal => null,
Post => Is_Empty'Result = (Node_Count (Container) = 1);
Ramification: An empty tree contains
just the root node.
{
AI12-0112-1}
function Node_Count (Container : Tree)
return Count_Type
with Nonblocking, Global =>
null, Use_Formal =>
null;
{
AI05-0136-1}
Node_Count returns the number of nodes in Container.
Ramification: Since all tree objects
have a root node, this can never return a value of 0. Node_Count (Some_Tree)
should always equal Subtree_Node_Count (Root (Some_Tree)).
{
AI12-0112-1}
function Subtree_Node_Count (Position : Cursor)
return Count_Type
with Nonblocking, Global =>
in all, Use_Formal =>
null);
{
AI05-0136-1}
{
AI05-0248-1}
If Position is No_Element, Subtree_Node_Count returns 0; otherwise, Subtree_Node_Count
returns the number of nodes in the subtree that is rooted by Position.
function Subtree_Node_Count (Container : Tree; Position : Cursor)
return Count_Type
with Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Nonblocking, Global => null, Use_Formal => null;
{
AI05-0136-1}
{
AI12-0112-1}
If Position is No_Element, Subtree_Node_Count returns 0; otherwise, Subtree_Node_Count
returns the number of nodes in the subtree of Container that is rooted
by Position.
Reason: {
AI12-0112-1}
We raise Program_Error if Position belongs to some other container because
we have promised to read only the container passed to this function.
Determining the answer requires reading the container that Position belongs
to, which we've promised not to do if it is not Container. We don't make
this check for functions like Has_Element and Is_Root which do not require
reading another container to determine the answer, but we do make it
for most functions.
{
AI12-0112-1}
function Depth (Position : Cursor)
return Count_Type
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
AI05-0136-1}
{
AI05-0248-1}
If Position equals No_Element, Depth returns 0; otherwise, Depth returns
the number of ancestor nodes of the node designated by Position (including
the node itself).
Ramification: Depth (Root (Some_Tree))
= 1.
function Depth (Container : Tree; Position : Cursor)
return Count_Type
with Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Nonblocking, Global => null, Use_Formal => null;
{
AI12-0112-1}
If Position equals No_Element, Depth returns 0; otherwise, Depth returns
the number of ancestor nodes of the node of Container designated by Position
(including the node itself).
{
AI12-0112-1}
function Is_Root (Position : Cursor)
return Boolean
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
AI05-0136-1}
{
AI05-0248-1}
Is_Root returns True if the Position designates the root node of some
tree; and returns False otherwise.
function Is_Root (Container : Tree; Position : Cursor)
return Boolean
with Nonblocking, Global => null, Use_Formal => null;
{
AI12-0112-1}
Is_Root returns True if the Position designates the root node of Container;
and returns False otherwise.
Ramification: The two parameter Is_Root
returns False even if Position is the root of some other tree than Container.
{
AI12-0112-1}
function Is_Leaf (Position : Cursor)
return Boolean
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
AI05-0136-1}
Is_Leaf returns True if Position designates a node that does not have
any child nodes; and returns False otherwise.
Ramification: Is_Leaf returns False if
passed No_Element, since No_Element does not designate a node. Is_Leaf
can be passed a cursor that designates the root node; Is_Leaf will return
True if passed the root node of an empty tree.
function Is_Leaf (Container : Tree; Position : Cursor)
return Boolean
with Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Nonblocking, Global => null, Use_Formal => null;
{
AI12-0112-1}
Is_Leaf returns True if Position designates a node in Container that
does not have any child nodes; and returns False otherwise.
function Is_Ancestor_Of (Container : Tree;
Parent : Cursor;
Position : Cursor) return Boolean
with Pre => (Meaningful_For (Container, Position)
or else raise Program_Error) and then
(Meaningful_For (Container, Parent)
or else raise Program_Error),
Nonblocking, Global => null, Use_Formal => null;
{
AI12-0112-1}
Is_Ancestor_Of returns True if Parent designates an ancestor node of
Position (including Position itself), and returns False otherwise.
{
AI12-0112-1}
function Root (Container : Tree)
return Cursor
with Nonblocking, Global =>
null, Use_Formal =>
null,
Post => Root'Result /= No_Element
and then
not Has_Element (Container, Root'Result);
{
AI05-0136-1}
Root returns a cursor that designates the root node of Container.
Ramification: There is always a root
node, even in an empty container, so this function never returns No_Element.
{
AI12-0112-1}
procedure Clear (Container :
in out Tree)
with Pre =>
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error,
Post => Node_Count (Container) = 1;
Ramification: The root node is not removed;
all trees have a root node.
function Element (Position : Cursor) return Element_Type
with Pre => (Position /= No_Element or else
raise Constraint_Error) and then
(Has_Element (Position) or else raise Program_Error),
Nonblocking, Global => in all, Use_Formal => Element_Type;
Ramification: The root node does not
contain an element, so that value cannot be read or written.
function Element (Container : Tree;
Position : Cursor) return Element_Type
with Pre => (Position /= No_Element
or else raise Constraint_Error) and then
(Has_Element (Container, Position)
or else raise Program_Error),
Nonblocking, Global => null, Use_Formal => Element_Type;
{
AI12-0112-1}
Element returns the element designated by Position in Container.
procedure Replace_Element (Container : in out Tree;
Position : in Cursor;
New_item : in Element_Type)
with Pre => (not Tampering_With_Elements_Prohibited (Container)
or else raise Program_Error) and then
(Position /= No_Element
or else raise Constraint_Error) and then
(Has_Element (Container, Position)
or else raise Program_Error);
{
AI05-0136-1}
{
AI05-0264-1}
{
AI12-0112-1}
{
AI12-0196-1}
Replace_Element assigns the value New_Item to the element designated
by Position. For the purposes of determining whether the parameters overlap
in a call to Replace_Element, the Container parameter is not considered
to overlap with any object [(including itself)].
procedure Query_Element
(Position : in Cursor;
Process : not null access procedure (Element : in Element_Type))
with Pre => (Position /= No_Element
or else raise Constraint_Error) and then
(Has_Element (Position)
or else raise Program_Error),
Global => in all;
{
AI05-0136-1}
{
AI05-0265-1}
{
AI12-0112-1}
Query_Element calls Process.
all with the element designated by
Position as the argument. Tampering with the elements of the tree that
contains the element designated by Position is prohibited during the
execution of the call on Process.
all. Any exception raised by
Process.
all is propagated.
procedure Query_Element
(Container : in Tree;
Position : in Cursor;
Process : not null access procedure (Element : in Element_Type))
with Pre => (Position /= No_Element
or else raise Constraint_Error) and then
(Has_Element (Container, Position)
or else raise Program_Error);
{
AI12-0112-1}
Query_Element calls Process.
all with the element designated by
Position as the argument. Tampering with the elements of Container is
prohibited during the execution of the call on Process.
all. Any
exception raised by Process.
all is propagated.
procedure Update_Element
(Container : in out Tree;
Position : in Cursor;
Process : not null access procedure
(Element : in out Element_Type))
with Pre => (Position /= No_Element
or else raise Constraint_Error) and then
(Has_Element (Container, Position)
or else raise Program_Error);
{
AI05-0136-1}
{
AI05-0264-1}
{
AI05-0265-1}
{
AI12-0112-1}
Update_Element calls Process.
all with the element designated by
Position as the argument. Tampering with the elements of Container is
prohibited during the execution of the call on Process.
all. Any
exception raised by Process.
all is propagated.
If Element_Type is unconstrained and definite,
then the actual Element parameter of Process.all shall be unconstrained.
Ramification: This means that the elements
cannot be directly allocated from the heap; it must be possible to change
the discriminants of the element in place.
{
AI12-0112-1}
type Constant_Reference_Type
(Element :
not null access constant Element_Type)
is private
with Implicit_Dereference => Element,
Nonblocking, Global =>
in out synchronized,
Default_Initial_Condition => (
raise Program_Error);
{
AI12-0112-1}
type Reference_Type (Element :
not null access Element_Type)
is private
with Implicit_Dereference => Element,
Nonblocking, Global =>
in out synchronized,
Default_Initial_Condition => (
raise Program_Error);
{
AI05-0212-1}
The types Constant_Reference_Type and Reference_Type need finalization.
Reason: It is expected that Reference_Type
(and Constant_Reference_Type) will be a controlled type, for which finalization
will have some action to terminate the tampering check for the associated
container. If the object is created by default, however, there is no
associated container. Since this is useless, and supporting this case
would take extra work, we define it to raise an exception.
{
AI12-0112-1}
function Constant_Reference (Container :
aliased in Tree;
Position :
in Cursor)
return Constant_Reference_Type
with Pre => (Position /= No_Element
or else raise Constraint_Error)
and then
(Has_Element (Container, Position)
or else raise Program_Error),
Post => Tampering_With_Cursors_Prohibited (Container),
Nonblocking, Global =>
null, Use_Formal =>
null;
{
AI05-0212-1}
{
AI05-0269-1}
This function (combined with the Constant_Indexing and Implicit_Dereference
aspects) provides a convenient way to gain read access to an individual
element of a tree given a cursor.
{
AI05-0212-1}
{
AI05-0265-1}
{
AI12-0112-1}
Constant_Reference returns an object whose discriminant is an access
value that designates the element designated by Position. Tampering with
the elements of Container is prohibited while the object returned by
Constant_Reference exists and has not been finalized.
{
AI12-0112-1}
function Reference (Container :
aliased in out Tree;
Position :
in Cursor)
return Reference_Type
with Pre => (Position /= No_Element
or else raise Constraint_Error)
and then
(Has_Element (Container, Position)
or else raise Program_Error),
Post => Tampering_With_Cursors_Prohibited (Container),
Nonblocking, Global =>
null, Use_Formal =>
null;
{
AI05-0212-1}
{
AI05-0269-1}
This function (combined with the Variable_Indexing and Implicit_Dereference
aspects) provides a convenient way to gain read and write access to an
individual element of a tree given a cursor.
{
AI05-0212-1}
{
AI05-0265-1}
{
AI12-0112-1}
Reference returns an object whose discriminant is an access value that
designates the element designated by Position. Tampering with the elements
of Container is prohibited while the object returned by Reference exists
and has not been finalized.
{
AI12-0112-1}
procedure Assign (Target :
in out Tree; Source :
in Tree)
with Pre =>
not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error,
Post => Node_Count (Source) = Node_Count (Target);
{
AI05-0136-1}
{
AI05-0248-1}
If Target denotes the same object as Source, the operation has no effect.
Otherwise, the elements of Source are copied to Target as for an
assignment_statement
assigning Source to Target.
Ramification: Each element in Target
has a parent element that corresponds to the parent element of the Source
element, and has child elements that correspond to the child elements
of the Source element.
Discussion: {
AI05-0005-1}
This routine exists for compatibility with the bounded tree container.
For an unbounded tree,
Assign(A, B) and
A := B behave
identically. For a bounded tree, := will raise an exception if the container
capacities are different, while Assign will not raise an exception if
there is enough room in the target.
{
AI12-0112-1}
function Copy (Source : Tree)
return Tree
with Post =>
Node_Count (Copy'Result) = Node_Count (Source)
and then
not Tampering_With_Elements_Prohibited (Copy'Result)
and then
not Tampering_With_Cursors_Prohibited (Copy'Result);
{
AI05-0136-1}
Returns a tree with the same structure as Source and whose elements are
initialized from the corresponding elements of Source.
{
AI12-0112-1}
procedure Move (Target :
in out Tree;
Source :
in out Tree)
with Pre => (
not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error)
and then
(
not Tampering_With_Cursors_Prohibited (Source)
or else raise Program_Error),
Post => (
if not Target'Has_Same_Storage (Source)
then
Node_Count (Target) = Node_Count (Source'Old)
and then
Node_Count (Source) = 1);
{
AI05-0136-1}
{
AI05-0248-1}
If Target denotes the same object as Source, then the operation has no
effect. Otherwise, Move first calls Clear (Target). Then, the nodes other
than the root node in Source are moved to Target (in the same positions).
After Move completes, Node_Count (Target) is the number of nodes originally
in Source, and Node_Count (Source) is 1.
procedure Delete_Leaf (Container : in out Tree;
Position : in out Cursor)
with Pre => (not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error) and then
(Position /= No_Element
or else raise Constraint_Error) and then
(Has_Element (Container, Position)
or else raise Program_Error) and then
(Is_Leaf (Container, Position)
or else raise Constraint_Error),
Post =>
Node_Count (Container)'Old = Node_Count (Container) + 1 and then
Position = No_Element;
Ramification: The check on Position checks
that the cursor does not belong to some other Container. This check implies
that a reference to the container is included in the cursor value. This
wording is not meant to require detection of dangling cursors; such cursors
are defined to be invalid, which means that execution is erroneous, and
any result is allowed (including not raising an exception).
The root node cannot be deleted.
procedure Delete_Subtree (Container : in out Tree;
Position : in out Cursor)
with Pre => (not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error) and then
(Position /= No_Element
or else raise Constraint_Error) and then
(Has_Element (Container, Position)
or else raise Program_Error),
Post => Node_Count (Container)'Old = Node_Count (Container) +
Subtree_Node_Count (Container, Position)'Old and then
Position = No_Element;
{
AI05-0136-1}
{
AI05-0264-1}
{
AI05-0269-1}
{
AI12-0112-1}
Delete_Subtree removes (from Container) the subtree designated by Position
(that is, all descendants of the node designated by Position including
the node itself), and Position is set to No_Element.
Ramification: The root node cannot be
deleted. To delete the entire contents of the tree, call Clear(Container).
procedure Swap (Container : in out Tree;
I, J : in Cursor)
with Pre => (not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error) and then
(I /= No_Element or else Constraint_Error) and then
(J /= No_Element or else Constraint_Error) and then
(Has_Element (Container, I)
or else raise Program_Error) and then
(Has_Element (Container, J)
or else raise Program_Error);
Ramification: After a call to Swap, I
designates the element value previously designated by J, and J designates
the element value previously designated by I. The position of the elements
do not change; for instance, the parent node and the first child node
of I are unchanged by the operation.
The root nodes do not contain element values,
so they cannot be swapped.
To be honest: The implementation is not
required to actually copy the elements if it can do the swap some other
way. But it is allowed to copy the elements if needed.
{
AI12-0112-1}
function Find (Container : Tree;
Item : Element_Type)
return Cursor
with Post => (
if Find'Result /= No_Element
then Has_Element (Container, Find'Result));
{
AI05-0136-1}
{
AI05-0262-1}
Find searches the elements of Container for an element equal to Item
(using the generic formal equality operator). The search starts at the
root node. The search traverses the tree in a depth-first order. If no
equal element is found, then Find returns No_Element. Otherwise, it returns
a cursor designating the first equal element encountered.
function Find_In_Subtree (Position : Cursor;
Item : Element_Type)
return Cursor
with Pre => Position /= No_Element or else raise Constraint_Error,
Post => (if Find_In_Subtree'Result = No_Element
then Has_Element (Find_In_Subtree'Result)),
Global => in all;
{
AI05-0136-1}
{
AI05-0248-1}
{
AI05-0262-1}
{
AI12-0112-1}
Find_In_Subtree searches the subtree rooted by Position for an element
equal to Item (using the generic formal equality operator). The search
starts at the element designated by Position. The search traverses the
subtree in a depth-first order. If no equal element is found, then Find
returns No_Element. Otherwise, it returns a cursor designating the first
equal element encountered.
Ramification: Find_In_Subtree does not
check any siblings of the element designated by Position. The root node
does not contain an element, and therefore it can never be returned,
but it can be explicitly passed to Position.
{
AI12-0112-1}
function Find_In_Subtree (Container : Tree;
Position : Cursor;
Item : Element_Type)
return Cursor
with Pre => (Position /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Position)
or else raise Program_Error),
Post => (
if Find_In_Subtree'Result = No_Element
then Has_Element (Container, Find_In_Subtree'Result));
{
AI12-0112-1}
Find_In_Subtree searches the subtree of Container rooted by Position
for an element equal to Item (using the generic formal equality operator).
The search starts at the element designated by Position. The search traverses
the subtree in a depth-first order. If no equal element is found, then
Find returns No_Element. Otherwise, it returns a cursor designating the
first equal element encountered.
function Ancestor_Find (Position : Cursor;
Item : Element_Type)
return Cursor
with Pre => Position /= No_Element or else raise Constraint_Error,
Post => (if Ancestor_Find'Result = No_Element
then Has_Element (Container, Ancestor_Find'Result)),
Global => in all;
{
AI05-0136-1}
{
AI05-0248-1}
{
AI12-0112-1}
Ancestor_Find searches for an element equal to Item (using the generic
formal equality operator). The search starts at the node designated by
Position, and checks each ancestor proceeding toward the root of the
subtree. If no equal element is found, then Ancestor_Find returns No_Element.
Otherwise, it returns a cursor designating the first equal element encountered.
Ramification: {
AI05-0248-1}
No_Element is returned if Position is the root node.
{
AI12-0112-1}
function Ancestor_Find (Container : Tree;
Position : Cursor;
Item : Element_Type)
return Cursor
with Pre => (Position /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Position)
or else raise Program_Error),
Post => (
if Ancestor_Find'Result = No_Element
then Has_Element (Container, Ancestor_Find'Result));
{
AI12-0112-1}
Ancestor_Find searches for an element equal to Item (using the generic
formal equality operator). The search starts at the node designated by
Position in Container, and checks each ancestor proceeding toward the
root of the subtree. If no equal element is found, then Ancestor_Find
returns No_Element. Otherwise, it returns a cursor designating the first
equal element encountered.
function Contains (Container : Tree;
Item : Element_Type) return Boolean;
{
AI05-0136-1}
Equivalent to Find (Container, Item) /= No_Element.
{
AI12-0112-1}
procedure Iterate
(Container :
in Tree;
Process :
not null access procedure (Position :
in Cursor))
with Allows_Exit;
{
AI05-0136-1}
{
AI05-0265-1}
{
AI12-0069-1}
Iterate calls Process.
all with a cursor that designates each element
in Container, starting from the root node and proceeding in a depth-first
order. Tampering with the cursors of Container is prohibited during the
execution of a call on Process.
all. Any exception raised by Process.
all
is propagated.
Ramification: Process is not called with
the root node, which does not have an associated element.
Implementation Note: The purpose of the
tamper with cursors check is to prevent erroneous execution from the
Position parameter of Process.all becoming invalid. This check
takes place when the operations that tamper with the cursors of the container
are called. The check cannot be made later (say in the body of Iterate),
because that could cause the Position cursor to be invalid and potentially
cause execution to become erroneous — defeating the purpose of
the check.
See Iterate for vectors (
A.18.2)
for a suggested implementation of the check.
procedure Iterate_Subtree
(Position : in Cursor;
Process : not null access procedure (Position : in Cursor))
with Allows_Exit,
Pre => Position /= No_Element or else raise Constraint_Error,
Global => in all;
{
AI05-0136-1}
{
AI05-0265-1}
{
AI12-0069-1}
{
AI12-0112-1}
Iterate_Subtree calls Process.
all with a cursor that designates
each element in the subtree rooted by the node designated by Position,
starting from the node designated by Position and proceeding in a depth-first
order. Tampering with the cursors of the tree that contains the element
designated by Position is prohibited during the execution of a call on
Process.
all. Any exception raised by Process.
all is propagated.
Ramification: Position can be passed
a cursor designating the root node; in that case, Process is not called
with the root node, which does not have an associated element.
procedure Iterate_Subtree
(Container : in Tree;
Position : in Cursor;
Process : not null access procedure (Position : in Cursor))
with Allows_Exit,
Pre => (Position /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Container, Position)
or else raise Program_Error);
{
AI12-0112-1}
Iterate_Subtree calls Process.
all with a cursor that designates
each element in the subtree rooted by the node designated by Position
in Container, starting from the node designated by Position and proceeding
in a depth-first order. Tampering with the cursors of the tree that contains
the element designated by Position is prohibited during the execution
of a call on Process.
all. Any exception raised by Process.
all
is propagated.
{
AI12-0112-1}
function Iterate (Container :
in Tree)
return Tree_Iterator_Interfaces.Parallel_Iterator'Class
with Post => Tampering_With_Cursors_Prohibited (Container);
{
AI05-0212-1}
{
AI05-0265-1}
{
AI05-0269-1}
{
AI12-0069-1}
{
AI12-0266-1}
Iterate returns an iterator object (see
5.5.1)
that will generate a value for a loop parameter (see
5.5.2)
designating each element in Container, starting from the root node and
proceeding in a depth-first order when used as a forward iterator, and
processing all nodes concurrently when used as a parallel iterator. Tampering
with the cursors of Container is prohibited while the iterator object
exists (in particular, in the
sequence_of_statements
of the
loop_statement
whose
iterator_specification
denotes this object). The iterator object needs finalization.
Discussion:
Exits are allowed from the loops created using the iterator objects.
In particular, to stop the iteration at a particular cursor, just add
exit when Cur = Stop;
in the body of
the loop (assuming that Cur is the loop parameter and Stop
is the cursor that you want to stop at).
function Iterate_Subtree (Position : in Cursor)
return Tree_Iterator_Interfaces.Parallel_Iterator'Class
with Pre => Position /= No_Element or else raise Constraint_Error,
Global => in all;
{
AI05-0212-1}
{
AI05-0265-1}
{
AI05-0269-1}
{
AI12-0069-1}
{
AI12-0112-1}
{
AI12-0266-1}
Iterate_Subtree returns an iterator object (see
5.5.1)
that will generate a value for a loop parameter (see
5.5.2)
designating each element in the subtree rooted by the node designated
by Position, starting from the node designated by Position and proceeding
in a depth-first order when used as a forward iterator, and processing
all nodes in the subtree concurrently when used as a parallel iterator.
Tampering with the cursors of the container that contains the node designated
by Position is prohibited while the iterator object exists (in particular,
in the
sequence_of_statements
of the
loop_statement
whose
iterator_specification
denotes this object). The iterator object needs finalization.
function Iterate_Subtree (Container : in Tree; Position : in Cursor)
return Tree_Iterator_Interfaces.Parallel_Iterator'Class
with Pre => (Position /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Container, Position)
or else raise Program_Error),
Post => Tampering_With_Cursors_Prohibited (Container);
{
AI12-0112-1}
Iterate_Subtree returns an iterator object (see
5.5.1)
that will generate a value for a loop parameter (see
5.5.2)
designating each element in the subtree rooted by the node designated
by Position in Container, starting from the node designated by Position
and proceeding in a depth-first order when used as a forward iterator,
and processing all nodes in the subtree concurrently when used as a parallel
iterator. Tampering with the cursors of the container that contains the
node designated by Position is prohibited while the iterator object exists
(in particular, in the
sequence_of_statements
of the
loop_statement
whose
iterator_specification
denotes this object). The iterator object needs finalization.
{
AI12-0112-1}
function Child_Count (Parent : Cursor)
return Count_Type
with Post => (
if Parent = No_Element
then Child_Count'Result = 0),
Nonblocking, Global =>
in all, Use_Formal =>
null;
{
AI05-0136-1}
Child_Count returns the number of child nodes of the node designated
by Parent.
function Child_Count (Container : Tree; Parent : Cursor)
return Count_Type
with Pre => Meaningful_For (Container, Parent)
or else raise Program_Error,
Post => (if Parent = No_Element then Child_Count'Result = 0),
Nonblocking, Global => null, Use_Formal => null;
{
AI12-0112-1}
Child_Count returns the number of child nodes of the node designated
by Parent in Container.
function Child_Depth (Parent, Child : Cursor) return Count_Type
with Pre => (Parent /= No_Element and then Child /= No_Element)
or else raise Constraint_Error,
Nonblocking, Global => in all, Use_Formal => null;
{
AI05-0136-1}
{
AI05-0262-1}
{
AI12-0112-1}
Child_Depth returns the number of ancestor nodes of Child (including
Child itself), up to but not including Parent; Program_Error is propagated
if Parent is not an ancestor of Child.
Ramification: Program_Error is propagated
if Parent and Child are nodes in different containers.
Child_Depth (Root (Some_Tree), Child) + 1 =
Depth (Child) as the root is not counted.
function Child_Depth (Container : Tree; Parent, Child : Cursor)
return Count_Type
with Pre => ((Parent /= No_Element and then Child /= No_Element)
or else raise Constraint_Error) and then
(Meaningful_For (Container, Parent)
or else raise Program_Error) and then
(Meaningful_For (Container, Child)
or else raise Program_Error),
Nonblocking, Global => null, Use_Formal => null;
{
AI12-0112-1}
Child_Depth returns the number of ancestor nodes of Child within Container
(including Child itself), up to but not including Parent; Program_Error
is propagated if Parent is not an ancestor of Child.
procedure Insert_Child (Container : in out Tree;
Parent : in Cursor;
Before : in Cursor;
New_Item : in Element_Type;
Count : in Count_Type := 1)
with Pre => (not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error) and then
(Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Container, Parent)
or else raise Program_Error) and then
(Meaningful_For (Container, Before)
or else raise Program_Error) and then
(Before = No_Element or else
Container.Parent (Before) = Parent
or else raise Constraint_Error),
Post => Node_Count (Container) =
Node_Count (Container)'Old + Count;
{
AI05-0136-1}
{
AI05-0248-1}
{
AI05-0262-1}
{
AI12-0112-1}
Insert_Child allocates Count nodes containing copies of New_Item and
inserts them as children of Parent. If Parent already has child nodes,
then the new nodes are inserted prior to the node designated by Before,
or, if Before equals No_Element, the new nodes are inserted after the
last existing child node of Parent. Any exception raised during allocation
of internal storage is propagated, and Container is not modified.
procedure Insert_Child (Container : in out Tree;
Parent : in Cursor;
Before : in Cursor;
New_Item : in Element_Type;
Position : out Cursor;
Count : in Count_Type := 1)
with Pre => (not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error) and then
(Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Container, Parent)
or else raise Program_Error) and then
(Meaningful_For (Container, Before)
or else raise Program_Error) and then
(Before = No_Element or else
Container.Parent (Before) = Parent
or else raise Constraint_Error),
Post => (Node_Count (Container) =
Node_Count (Container)'Old + Count) and then
Has_Element (Container, Position);
{
AI05-0136-1}
{
AI05-0248-1}
{
AI05-0257-1}
{
AI05-0262-1}
{
AI12-0112-1}
Insert_Child allocates Count nodes containing copies of New_Item and
inserts them as children of Parent. If Parent already has child nodes,
then the new nodes are inserted prior to the node designated by Before,
or, if Before equals No_Element, the new nodes are inserted after the
last existing child node of Parent. Position designates the first newly-inserted
node, or if Count equals 0, then Position is assigned the value of Before.
Any exception raised during allocation of internal storage is propagated,
and Container is not modified.
procedure Insert_Child (Container : in out Tree;
Parent : in Cursor;
Before : in Cursor;
Position : out Cursor;
Count : in Count_Type := 1)
with Pre => (not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error) and then
(Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Container, Parent)
or else raise Program_Error) and then
(Meaningful_For (Container, Before)
or else raise Program_Error) and then
(Before = No_Element or else
Container.Parent (Before) = Parent
or else raise Constraint_Error),
Post => (Node_Count (Container) =
Node_Count (Container)'Old + Count) and then
Has_Element (Container, Position);
{
AI05-0136-1}
{
AI05-0257-1}
{
AI05-0262-1}
{
AI05-0264-1}
{
AI12-0112-1}
Insert_Child allocates Count nodes, the elements contained in the new
nodes are initialized by default (see
3.3.1),
and the new nodes are inserted as children of Parent. If Parent already
has child nodes, then the new nodes are inserted prior to the node designated
by Before, or, if Before equals No_Element, the new nodes are inserted
after the last existing child node of Parent. Position designates the
first newly-inserted node, or if Count equals 0, then Position is assigned
the value of Before. Any exception raised during allocation of internal
storage is propagated, and Container is not modified.
{
AI12-0112-1}
procedure Prepend_Child (Container :
in out Tree;
Parent :
in Cursor;
New_Item :
in Element_Type;
Count :
in Count_Type := 1)
with Pre => (
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error)
and then
(Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error),
Post => Node_Count (Container) =
Node_Count (Container)'Old + Count;
{
AI05-0136-1}
Equivalent to Insert_Child (Container, Parent, First_Child (Container,
Parent), New_Item, Count).
{
AI12-0112-1}
procedure Append_Child (Container :
in out Tree;
Parent :
in Cursor;
New_Item :
in Element_Type;
Count :
in Count_Type := 1)
with Pre => (
not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error)
and then
(Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error),
Post => Node_Count (Container) =
Node_Count (Container)'Old + Count;
procedure Delete_Children (Container : in out Tree;
Parent : in Cursor)
with Pre => (not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error) and then
(Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Container, Parent)
or else raise Program_Error),
Post => (Node_Count (Container) = Node_Count (Container)'Old -
Child_Count (Container, Parent)'Old) and then
Child_Count (Container, Parent) = 0;
{
AI05-0136-1}
{
AI12-0112-1}
Delete_Children removes (from Container) all of the descendants of Parent
other than Parent itself.
Discussion: This routine deletes all
of the child subtrees of Parent at once. Use Delete_Subtree to delete
an individual subtree.
procedure Copy_Subtree (Target : in out Tree;
Parent : in Cursor;
Before : in Cursor;
Source : in Cursor)
with Pre => (not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error) and then
(Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Target, Parent)
or else raise Program_Error) and then
(Meaningful_For (Target, Before)
or else raise Program_Error) and then
(Before = No_Element or else
Target.Parent (Before) = Parent
or else raise Constraint_Error) and then
(not Is_Root (Source)
or else raise Constraint_Error),
Post => Node_Count (Target) =
Node_Count (Target)'Old + Subtree_Node_Count (Source),
Global => in all;
{
AI05-0136-1}
{
AI05-0248-1}
{
AI05-0262-1}
{
AI12-0112-1}
If Source is equal to No_Element, then the operation has no effect. Otherwise,
the subtree rooted by Source (which can be from any tree; it does not
have to be a subtree of Target) is copied (new nodes are allocated to
create a new subtree with the same structure as the Source subtree, with
each element initialized from the corresponding element of the Source
subtree) and inserted into Target as a child of Parent. If Parent already
has child nodes, then the new nodes are inserted prior to the node designated
by Before, or, if Before equals No_Element, the new nodes are inserted
after the last existing child node of Parent. The parent of the newly
created subtree is set to Parent, and the overall count of Target is
incremented by Subtree_Node_Count (Source). Any exception raised during
allocation of internal storage is propagated, and Container is not modified.
Discussion: {
AI12-0112-1}
We only need one routine here, as the source object is not modified,
so we can use the same routine for both copying within and between containers.
However, that requires a contract that allows reading of any container
of the correct type, so we provide two other routines wuth more restrictive
contracts.
Ramification: We do not allow copying
a subtree that includes a root node, as that would require inserting
a node with no value in the middle of the target tree. To copy an entire
tree to another tree object, use Copy.
procedure Copy_Local_Subtree (Target : in out Tree;
Parent : in Cursor;
Before : in Cursor;
Source : in Cursor)
with Pre => (not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error) and then
(Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Target, Parent)
or else raise Program_Error) and then
(Meaningful_For (Target, Before)
or else raise Program_Error) and then
(Before = No_Element or else
Target.Parent (Before) = Parent
or else raise Constraint_Error) and then
(Meaningful_For (Target, Source)
or else raise Program_Error) and then
(not Is_Root (Source)
or else raise Constraint_Error),
Post => Node_Count (Target) = Node_Count (Target)'Old +
Subtree_Node_Count (Target, Source);
{
AI12-0112-1}
If Source is equal to No_Element, then the operation has no effect. Otherwise,
the subtree rooted by Source in Target is copied (new nodes are allocated
to create a new subtree with the same structure as the Source subtree,
with each element initialized from the corresponding element of the Source
subtree) and inserted into Target as a child of Parent. If Parent already
has child nodes, then the new nodes are inserted prior to the node designated
by Before, or, if Before equals No_Element, the new nodes are inserted
after the last existing child node of Parent. The parent of the newly
created subtree is set to Parent. Any exception raised during allocation
of internal storage is propagated, and Container is not modified.
procedure Copy_Subtree (Target : in out Tree;
Parent : in Cursor;
Before : in Cursor;
Source : in Tree;
Subtree : in Cursor)
with Pre => (not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error) and then
(Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Target, Parent)
or else raise Program_Error) and then
(Meaningful_For (Target, Before)
or else raise Program_Error) and then
(Before = No_Element or else
Target.Parent (Before) = Parent
or else raise Constraint_Error) and then
(Meaningful_For (Source, Subtree)
or else raise Program_Error) and then
(not Is_Root (Source, Subtree)
or else raise Constraint_Error),
Post => Node_Count (Target) = Node_Count (Target)'Old +
Subtree_Node_Count (Source, Subtree);
{
AI12-0112-1}
If Subtree is equal to No_Element, then the operation has no effect.
Otherwise, the subtree rooted by Subtree in Source is copied (new nodes
are allocated to create a new subtree with the same structure as the
Subtree, with each element initialized from the corresponding element
of the Subtree) and inserted into Target as a child of Parent. If Parent
already has child nodes, then the new nodes are inserted prior to the
node designated by Before, or, if Before equals No_Element, the new nodes
are inserted after the last existing child node of Parent. The parent
of the newly created subtree is set to Parent. Any exception raised during
allocation of internal storage is propagated, and Container is not modified.
procedure Splice_Subtree (Target : in out Tree;
Parent : in Cursor;
Before : in Cursor;
Source : in out Tree;
Position : in out Cursor)
with Pre => (not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error) and then
(not Tampering_With_Cursors_Prohibited (Source)
or else raise Program_Error) and then
(Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Target, Parent)
or else raise Program_Error) and then
(Meaningful_For (Target, Before)
or else raise Program_Error) and then
(Before = No_Element or else
Target.Parent (Before) /= Parent
or else raise Constraint_Error) and then
(Position /= No_Element
or else raise Constraint_Error) and then
(Has_Element (Source, Position)
or else raise Program_Error) and then
(Target'Has_Same_Storage (Source) or else
Position = Before or else
Is_Ancestor_Of (Target, Position, Parent)
or else raise Constraint_Error),
Post => (declare
Org_Sub_Count renames
Subtree_Node_Count (Source, Position)'Old;
Org_Target_Count renames Node_Count (Target)'Old;
begin
(if not Target'Has_Same_Storage (Source) then
Node_Count (Target) = Org_Target_Count +
Org_Sub_Count and then
Node_Count (Source) = Node_Count (Source)'Old -
Org_Sub_Count and then
Has_Element (Target, Position)
else
Target.Parent (Position) = Parent and then
Node_Count (Target) = Org_Target_Count));
{
AI05-0136-1}
{
AI05-0248-1}
{
AI05-0262-1}
{
AI05-0269-1}
{
AI12-0112-1}
If Source denotes the same object as Target, then: if Position equals
Before there is no effect; otherwise, the subtree rooted by the element
designated by Position is moved to be a child of Parent. If Parent already
has child nodes, then the moved nodes are inserted prior to the node
designated by Before, or, if Before equals No_Element, the moved nodes
are inserted after the last existing child node of Parent. In each of
these cases, Position and the count of Target are unchanged, and the
parent of the element designated by Position is set to Parent.
Reason: We can't allow moving the subtree
of Position to a proper descendant node of the subtree, as the descendant
node will be part of the subtree being moved. The result would be a circularly
linked tree, or one with inaccessible nodes. Thus we have to check Position
against Parent, even though such a check is O(Depth(Source)).
{
AI05-0136-1}
{
AI05-0248-1}
Otherwise (if Source does not denote the same object as Target), the
subtree designated by Position is removed from Source and moved to Target.
The subtree is inserted as a child of Parent. If Parent already has child
nodes, then the moved nodes are inserted prior to the node designated
by Before, or, if Before equals No_Element, the moved nodes are inserted
after the last existing child node of Parent. In each of these cases,
the count of Target is incremented by Subtree_Node_Count (Position),
and the count of Source is decremented by Subtree_Node_Count (Position),
Position is updated to represent an element in Target.
Ramification: If Source is the same as
Target, and Position = Before, or Next_Sibling(Position) = Before, Splice_Subtree
has no effect, as the subtree does not have to move to meet the postcondition.
We do not allow splicing a subtree that includes
a root node, as that would require inserting a node with no value in
the middle of the target tree. Splice the children of the root node instead.
For this reason there is no operation to splice
an entire tree, as that would necessarily involve splicing a root node.
procedure Splice_Subtree (Container: in out Tree;
Parent : in Cursor;
Before : in Cursor;
Position : in Cursor)
with Pre => (not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error) and then
(Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Container, Parent)
or else raise Program_Error) and then
(Meaningful_For (Container, Before)
or else raise Program_Error) and then
(Before = No_Element or else
Container.Parent (Before) /= Parent
or else raise Constraint_Error) and then
(Position /= No_Element
or else raise Constraint_Error) and then
(Has_Element (Container, Position)
or else raise Program_Error) and then
(Position = Before or else
Is_Ancestor_Of (Container, Position, Parent)
or else raise Constraint_Error),
Post => (Node_Count (Container) =
Node_Count (Container)'Old and then
Container.Parent (Position) = Parent);
{
AI05-0136-1}
{
AI05-0248-1}
{
AI05-0262-1}
{
AI05-0269-1}
{
AI12-0112-1}
If Position equals Before, there is no effect. Otherwise, the subtree
rooted by the element designated by Position is moved to be a child of
Parent. If Parent already has child nodes, then the moved nodes are inserted
prior to the node designated by Before, or, if Before equals No_Element,
the moved nodes are inserted after the last existing child node of Parent.
The parent of the element designated by Position is set to Parent.
Reason: We can't allow moving the subtree
of Position to a proper descendant node of the subtree, as the descendant
node will be part of the subtree being moved.
procedure Splice_Children (Target : in out Tree;
Target_Parent : in Cursor;
Before : in Cursor;
Source : in out Tree;
Source_Parent : in Cursor)
with Pre => (not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error) and then
(not Tampering_With_Cursors_Prohibited (Source)
or else raise Program_Error) and then
(Target_Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Target, Target_Parent)
or else raise Program_Error) and then
(Meaningful_For (Target, Before)
or else raise Program_Error) and then
(Source_Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Source, Source_Parent)
or else raise Program_Error) and then
(Before = No_Element or else
Parent (Target, Before) /= Target_Parent
or else raise Constraint_Error) and then
(Target'Has_Same_Storage (Source) or else
Target_Parent = Source_Parent or else
Is_Ancestor_Of (Target, Source_Parent, Target_Parent)
or else raise Constraint_Error),
Post => (declare
Org_Child_Count renames
Child_Count (Source, Source_Parent)'Old;
Org_Target_Count renames Node_Count (Target)'Old;
begin
(if not Target'Has_Same_Storage (Source) then
Node_Count (Target) = Org_Target_Count +
Org_Child_Count and then
Node_Count (Source) = Node_Count (Source)'Old -
Org_Child_Count
else
Node_Count (Target) = Org_Target_Count));
If Source denotes
the same object as Target, then:
if Target_Parent equals Source_Parent
there is no effect; else
{
AI05-0136-1}
{
AI05-0248-1}
{
AI05-0269-1}
the child elements (and the further descendants) of Source_Parent are
moved to be child elements of Target_Parent. If Target_Parent already
has child elements, then the moved elements are inserted prior to the
node designated by Before, or, if Before equals No_Element, the moved
elements are inserted after the last existing child node of Target_Parent.
The parent of each moved child element is set to Target_Parent.
Reason: We can't allow moving the children
of Source_Parent to a proper descendant node, as the descendant node
will be part of one of the subtrees being moved.
{
AI05-0136-1}
{
AI05-0248-1}
{
AI05-0269-1}
Otherwise (if Source does not denote the same object as Target), the
child elements (and the further descendants) of Source_Parent are removed
from Source and moved to Target. The child elements are inserted as children
of Target_Parent. If Target_Parent already has child elements, then the
moved elements are inserted prior to the node designated by Before, or,
if Before equals No_Element, the moved elements are inserted after the
last existing child node of Target_Parent. In each of these cases, the
overall count of Target is incremented by Subtree_Node_Count (Source_Parent)-1,
and the overall count of Source is decremented by Subtree_Node_Count
(Source_Parent)-1.
Ramification: The node designated by
Source_Parent is not moved, thus we never need to update Source_Parent.
Move (Target, Source) could be written Splice_Children
(Target, Target.Root, No_Element, Source, Source.Root);
procedure Splice_Children (Container : in out Tree;
Target_Parent : in Cursor;
Before : in Cursor;
Source_Parent : in Cursor)
with Pre => (not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error) and then
(Target_Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Container, Target_Parent)
or else raise Program_Error) and then
(Meaningful_For (Container, Before)
or else raise Program_Error) and then
(Source_Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Container, Source_Parent)
or else raise Program_Error) and then
(Before = No_Element or else
Parent (Container, Before) /= Target_Parent
or else raise Constraint_Error) and then
(Target_Parent = Source_Parent or else
Is_Ancestor_Of (Container, Source_Parent, Target_Parent)
or else raise Constraint_Error),
Post => Node_Count (Container) = Node_Count (Container)'Old;
{
AI05-0136-1}
{
AI05-0248-1}
{
AI05-0262-1}
{
AI05-0264-1}
{
AI05-0269-1}
{
AI12-0112-1}
If Target_Parent equals Source_Parent there is no effect. Otherwise,
the child elements (and the further descendants) of Source_Parent are
moved to be child elements of Target_Parent. If Target_Parent already
has child elements, then the moved elements are inserted prior to the
node designated by Before, or, if Before equals No_Element, the moved
elements are inserted after the last existing child node of Target_Parent.
The parent of each moved child element is set to Target_Parent.
function Parent (Position : Cursor) return Cursor
with Nonblocking, Global => in all, Use_Formal => null,
Post => (if Position = No_Element or else
Is_Root (Position) then Parent'Result = No_Element);
function Parent (Container : Tree;
Position : Cursor) return Cursor
with Nonblocking, Global => null, Use_Formal => null,
Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Post => (if Position = No_Element or else
Is_Root (Container, Position)
then Parent'Result = No_Element
else Has_Element (Container, Parent'Result));
{
AI12-0112-1}
Returns a cursor designating the parent node of the node designated by
Position in Container.
function First_Child (Parent : Cursor) return Cursor
with Nonblocking, Global => in all, Use_Formal => null,
Pre => Parent /= No_Element or else raise Constraint_Error;
{
AI05-0136-1}
{
AI12-0112-1}
First_Child returns a cursor designating the first child node of the
node designated by Parent; if there is no such node, No_Element is returned.
function First_Child (Container : Tree;
Parent : Cursor) return Cursor
with Nonblocking, Global => null, Use_Formal => null,
Pre => (Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Container, Parent)
or else raise Program_Error),
Post => First_Child'Result = No_Element or else
Has_Element (Container, First_Child'Result);
{
AI12-0112-1}
First_Child returns a cursor designating the first child node of the
node designated by Parent in Container; if there is no such node, No_Element
is returned.
{
AI12-0112-1}
function First_Child_Element (Parent : Cursor)
return Element_Type
with Nonblocking, Global =>
in all, Use_Formal => Element_Type,
Pre => (Parent /= No_Element
and then
Last_Child (Parent) /= No_Element)
or else raise Constraint_Error;
{
AI05-0136-1}
Equivalent to Element (First_Child (Parent)).
function First_Child_Element (Container : Tree;
Parent : Cursor) return Element_Type
with Nonblocking, Global => null, Use_Formal => Element_Type,
Pre => (Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Container, Parent)
or else raise Program_Error) and then
(First_Child (Container, Parent) /= No_Element
or else raise Constraint_Error);
{
AI12-0112-1}
Equivalent to Element (Container, First_Child (Container, Parent)).
function Last_Child (Parent : Cursor) return Cursor
with Nonblocking, Global => in all, Use_Formal => null,
Pre => Parent /= No_Element or else raise Constraint_Error;
{
AI05-0136-1}
{
AI12-0112-1}
Last_Child returns a cursor designating the last child node of the node
designated by Parent; if there is no such node, No_Element is returned.
function Last_Child (Container : Tree;
Parent : Cursor) return Cursor
with Nonblocking, Global => null, Use_Formal => null,
Pre => (Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Container, Parent)
or else raise Program_Error),
Post => Last_Child'Result = No_Element or else
Has_Element (Container, Last_Child'Result);
{
AI12-0112-1}
Last_Child returns a cursor designating the last child node of the node
designated by Parent in Container; if there is no such node, No_Element
is returned.
{
AI12-0112-1}
function Last_Child_Element (Parent : Cursor)
return Element_Type
with Nonblocking, Global =>
in all, Use_Formal => Element_Type,
Pre => (Parent /= No_Element
and then
Last_Child (Parent) /= No_Element)
or else raise Constraint_Error;
{
AI05-0136-1}
Equivalent to Element (Last_Child (Parent)).
function Last_Child_Element (Container : Tree;
Parent : Cursor) return Element_Type
with Nonblocking, Global => null, Use_Formal => Element_Type,
Pre => (Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Container, Parent)
or else raise Program_Error) and then
(Last_Child (Container, Parent) /= No_Element
or else raise Constraint_Error);
{
AI12-0112-1}
Equivalent to Element (Container, Last_Child (Container, Parent)).
{
AI12-0112-1}
function Next_Sibling (Position : Cursor)
return Cursor
with Nonblocking, Global =>
in all, Use_Formal =>
null,
Post => (
if Position = No_Element
then Next_Sibling'Result = No_Element);
{
AI05-0136-1}
If Position equals No_Element or designates the last child node of its
parent, then Next_Sibling returns the value No_Element. Otherwise, it
returns a cursor that designates the successor (with the same parent)
of the node designated by Position.
function Next_Sibling (Container : Tree;
Position : Cursor) return Cursor
with Nonblocking, Global => null, Use_Formal => null,
Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Post => (if Next_Sibling'Result = No_Element then
Position = No_Element or else
Is_Root (Container, Position) or else
Last_Child (Container, Parent (Container, Position))
= Position
else Has_Element (Container, Next_Sibling'Result));
{
AI12-0112-1}
Next_Sibling returns a cursor that designates the successor (with the
same parent) of the node designated by Position in Container.
{
AI12-0112-1}
function Previous_Sibling (Position :
in out Cursor)
with Nonblocking, Global =>
in all, Use_Formal =>
null,
Post => (
if Position = No_Element
then Previous_Sibling'Result = No_Element);
{
AI05-0136-1}
If Position equals No_Element or designates the first child node of its
parent, then Previous_Sibling returns the value No_Element. Otherwise,
it returns a cursor that designates the predecessor (with the same parent)
of the node designated by Position.
function Previous_Sibling (Container : Tree;
Position : Cursor) return Cursor
with Nonblocking, Global => null, Use_Formal => null,
Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Post => (if Previous_Sibling'Result = No_Element then
Position = No_Element or else
Is_Root (Container, Position) or else
First_Child (Container, Parent (Container, Position))
= Position
else Has_Element (Container, Previous_Sibling'Result));
{
AI12-0112-1}
Previous_Sibling returns a cursor that designates the predecessor (with
the same parent) of the node designated by Position in Container.
{
AI12-0112-1}
procedure Next_Sibling (Position :
in out Cursor)
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
AI05-0136-1}
Equivalent to Position := Next_Sibling (Position);
procedure Next_Sibling (Container : in Tree;
Position : in out Cursor)
with Nonblocking, Global => null, Use_Formal => null,
Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Post => (if Position /= No_Element
then Has_Element (Container, Position));
{
AI12-0112-1}
Equivalent to Position := Next_Sibling (Container, Position);
{
AI12-0112-1}
procedure Previous_Sibling (Position :
in out Cursor)
with Nonblocking, Global =>
in all, Use_Formal =>
null;
{
AI05-0136-1}
Equivalent to Position := Previous_Sibling (Position);
procedure Previous_Sibling (Container : in Tree;
Position : in out Cursor)
with Nonblocking, Global => null, Use_Formal => null,
Pre => Meaningful_For (Container, Position)
or else raise Program_Error,
Post => (if Position /= No_Element
then Has_Element (Container, Position);
{
AI12-0112-1}
Equivalent to Position := Previous_Sibling (Container, Position);
{
AI12-0112-1}
procedure Iterate_Children
(Parent :
in Cursor;
Process :
not null access procedure (Position :
in Cursor))
with Allows_Exit,
Pre => Parent /= No_Element
or else raise Constraint_Error,
Global =>
in all, Use_Formal =>
null;
Iterate_Children calls Process.all with
a cursor that designates each child node of Parent, starting with the
first child node and moving the cursor as per the Next_Sibling function.
{
AI05-0265-1}
Tampering with the cursors of the tree containing Parent is prohibited
during the execution of a call on Process.
all. Any exception raised
by Process.
all is propagated.
{
AI12-0112-1}
procedure Iterate_Children
(Container :
in Tree;
Parent :
in Cursor;
Process :
not null access procedure (Position :
in Cursor))
with Allows_Exit,
Pre => (Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error);
{
AI12-0112-1}
Iterate_Children calls Process.
all with a cursor that designates
each child node of Container and Parent, starting with the first child
node and moving the cursor as per the Next_Sibling function.
{
AI12-0112-1}
Tampering with the cursors of the tree containing Parent is prohibited
during the execution of a call on Process.
all. Any exception raised
by Process.
all is propagated.
{
AI12-0112-1}
procedure Reverse_Iterate_Children
(Parent :
in Cursor;
Process :
not null access procedure (Position :
in Cursor))
with Allows_Exit,
Pre => Parent /= No_Element
or else raise Constraint_Error,
Global =>
in all, Use_Formal =>
null;
Reverse_Iterate_Children calls Process.all
with a cursor that designates each child node of Parent, starting with
the last child node and moving the cursor as per the Previous_Sibling
function.
{
AI05-0265-1}
Tampering with the cursors of the tree containing Parent is prohibited
during the execution of a call on Process.
all. Any exception raised
by Process.
all is propagated.
{
AI12-0112-1}
procedure Reverse_Iterate_Children
(Container :
in Tree;
Parent :
in Cursor;
Process :
not null access procedure (Position :
in Cursor))
with Allows_Exit,
Pre => (Parent /= No_Element
or else raise Constraint_Error)
and then
(Meaningful_For (Container, Parent)
or else raise Program_Error);
{
AI12-0112-1}
Reverse_Iterate_Children calls Process.
all with a cursor that
designates each child node of Container and Parent, starting with the
last child node and moving the cursor as per the Previous_Sibling function.
{
AI12-0112-1}
Tampering with the cursors of the tree containing Parent is prohibited
during the execution of a call on Process.
all. Any exception raised
by Process.
all is propagated.
function Iterate_Children (Container : in Tree; Parent : in Cursor)
return Tree_Iterator_Interfaces.Parallel_Reversible_Iterator'Class
with Pre => (Parent /= No_Element
or else raise Constraint_Error) and then
(Meaningful_For (Container, Parent)
or else raise Program_Error),
Post => Tampering_With_Cursors_Prohibited (Container);
{
AI05-0212-1}
{
AI05-0265-1}
{
AI12-0112-1}
{
AI12-0266-1}
Iterate_Children returns an iterator object (see
5.5.1)
that will generate a value for a loop parameter (see
5.5.2)
designating each child node of Parent. When used as a forward iterator,
the nodes are designated starting with the first child node and moving
the cursor as per the function Next_Sibling; when used as a reverse iterator,
the nodes are designated starting with the last child node and moving
the cursor as per the function Previous_Sibling; when used as a parallel
iterator, processing all child nodes concurrently. Tampering with the
cursors of Container is prohibited while the iterator object exists (in
particular, in the
sequence_of_statements
of the
loop_statement
whose
iterator_specification
denotes this object). The iterator object needs finalization.
{
AI12-0111-1}
The nested package Multiway_Trees.Stable provides a type Stable.Tree
that represents a
stable tree,
which is one
that cannot grow and shrink. Such a tree can be created by calling the
Copy function, or by establishing a
stabilized view of an ordinary
tree.
{
AI12-0111-1}
The subprograms of package Containers.Multiway_Trees that have a parameter
or result of type tree are included in the nested package Stable with
the same specification, except that the following are omitted:
Tampering_With_Cursors_Prohibited, Tampering_With_Elements_Prohibited,
Assign, Move, Clear, Delete_Leaf, Insert_Child, Delete_Children, Delete_Subtree,
Copy_Subtree, Copy_Local_Subtree, Splice_Subtree, and Splice_Children
Ramification: The names Tree and Cursor
mean the types declared in the nested package in these subprogram specifications.
Reason: The omitted routines are those
that tamper with cursors or elements (or test that state). The model
is that it is impossible to tamper with cursors or elements of a stable
view since no such operations are included. Thus tampering checks are
not needed for a stable view, and we omit the operations associated with
those checks.
{
AI12-0111-1}
The operations of this package are equivalent to those for ordinary trees,
except that the calls to Tampering_With_Cursors_Prohibited and Tampering_With_Elements_Prohibited
that occur in preconditions are replaced by False, and any that occur
in postconditions are replaced by True.
{
AI12-0111-1}
{
AI12-0439-1}
If a stable tree is declared with the Base discriminant designating a
pre-existing ordinary tree, the stable tree represents a stabilized view
of the underlying ordinary tree, and any operation on the stable tree
is reflected on the underlying ordinary tree. While a stabilized view
exists, any operation that tampers with elements performed on the underlying
tree is prohibited. The finalization of a stable tree that provides such
a view removes this restriction on the underlying ordinary tree [(though
some other restriction can exist due to other concurrent iterations or
stabilized views)].
{
AI12-0111-1}
{
AI12-0438-1}
If a stable tree is declared without specifying Base, the object is necessarily
initialized. The initializing expression of the stable tree, [typically
a call on Copy], determines the Node_Count of the tree. The Node_Count
of a stable tree never changes after initialization.
Proof: {
AI12-0438-1}
Initialization is required as the type is indefinite, see
3.3.1.
Bounded (Run-Time) Errors
{
AI05-0136-1}
{
AI05-0248-1}
It is a bounded error for the actual function associated
with a generic formal subprogram, when called as part of an operation
of this package, to tamper with elements of any Tree parameter of the
operation. Either Program_Error is raised, or the operation works as
defined on the value of the Tree either prior to, or subsequent to, some
or all of the modifications to the Tree.
{
AI05-0136-1}
It is a bounded error to call any subprogram declared
in the visible part of Containers.Multiway_Trees when the associated
container has been finalized. If the operation takes Container as an
in out parameter, then it raises Constraint_Error or Program_Error.
Otherwise, the operation either proceeds as it would for an empty container,
or it raises Constraint_Error
or Program_Error.
Erroneous Execution
{
AI05-0136-1}
A Cursor value is
invalid if any of the following have occurred
since it was created:
The tree that contains the element it designates
has been finalized;
The tree that contains the element it designates
has been used as the Source or Target of a call to Move;
The tree that contains the element it designates
has been used as the Target of a call to Assign or the target of an
assignment_statement;
The element it designates has been removed from
the tree that previously contained the element.
Reason: We talk about which tree the
element was removed from in order to handle splicing nodes from one tree
to another. The node still exists, but any cursors that designate it
in the original tree are now invalid. This bullet covers removals caused
by calls to Clear, Delete_Leaf, Delete_Subtree, Delete_Children, Splice_Children,
and Splice_Subtree.
The result of "=" or Has_Element is unspecified
if it is called with an invalid cursor parameter.
Execution is erroneous if any other subprogram declared in Containers.Multiway_Trees
is called with an invalid cursor parameter.
Discussion: The list above is intended
to be exhaustive. In other cases, a cursor value continues to designate
its original element (or the root node). For instance, cursor values
survive the insertion and deletion of other nodes.
While it is possible to check for these cases,
in many cases the overhead necessary to make the check is substantial
in time or space. Implementations are encouraged to check for as many
of these cases as possible and raise Program_Error if detected.
{
AI05-0212-1}
Execution is erroneous if the tree associated with the result of a call
to Reference or Constant_Reference is finalized before the result object
returned by the call to Reference or Constant_Reference is finalized.
Reason: Each object of Reference_Type
and Constant_Reference_Type probably contains some reference to the originating
container. If that container is prematurely finalized (which is only
possible via Unchecked_Deallocation, as accessibility checks prevent
passing a container to Reference that will not live as long as the result),
the finalization of the object of Reference_Type will try to access a
nonexistent object. This is a normal case of a dangling pointer created
by Unchecked_Deallocation; we have to explicitly mention it here as the
pointer in question is not visible in the specification of the type.
(This is the same reason we have to say this for invalid cursors.)
Implementation Requirements
{
AI05-0136-1}
No storage associated with a multiway tree object shall be lost upon
assignment or scope exit.
{
AI05-0136-1}
{
AI05-0262-1}
The execution of an
assignment_statement
for a tree shall have the effect of copying the elements from the source
tree object to the target tree object and changing the node count of
the target object to that of the source object.
Implementation Note: {
AI05-0298-1}
An assignment of a Tree is a “deep” copy; that is the elements
are copied as well the data structures. We say “effect of”
in order to allow the implementation to avoid copying elements immediately
if it wishes. For instance, an implementation that avoided copying until
one of the containers is modified would be allowed. (Note that this implementation
would require care, see
A.18.2 for more.)
Implementation Advice
{
AI05-0136-1}
Containers.Multiway_Trees should be implemented similarly to a multiway
tree. In particular, if
N is the overall number of nodes for a
particular tree, then the worst-case time complexity of Element, Parent,
First_Child, Last_Child, Next_Sibling, Previous_Sibling, Insert_Child
with Count=1, and Delete should be
O(log
N).
Implementation Advice: The worst-case
time complexity of the Element, Parent, First_Child, Last_Child, Next_Sibling,
Previous_Sibling, Insert_Child with Count=1, and Delete operations of
Containers.Multiway_Trees should be O(log N).
Reason: We do not mean to overly constrain
implementation strategies here. However, it is important for portability
that the performance of large containers has roughly the same factors
on different implementations. If a program is moved to an implementation
that takes O(N) time to access elements, that program could
be unusable when the trees are large. We allow O(log N)
access because the proportionality constant and caching effects are likely
to be larger than the log factor, and we don't want to discourage innovative
implementations.
{
AI05-0136-1}
Move should not copy elements, and should minimize copying of internal
data structures.
Implementation Advice: Containers.Multiway_Trees.Move
should not copy elements, and should minimize copying of internal data
structures.
Implementation Note: Usually that can
be accomplished simply by moving the pointer(s) to the internal data
structures from the Source container to the Target container.
{
AI05-0136-1}
If an exception is propagated from a tree operation, no storage should
be lost, nor any elements removed from a tree unless specified by the
operation.
Implementation Advice: If an exception
is propagated from a tree operation, no storage should be lost, nor any
elements removed from a tree unless specified by the operation.
Reason: This is important so that programs
can recover from errors. But we don't want to require heroic efforts,
so we just require documentation of cases where this can't be accomplished.
Extensions to Ada 2005
Inconsistencies With Ada 2012
{
AI12-0111-1}
Correction: Tampering with elements is now
defined to be equivalent to tampering with cursors for ordinary containers.
If a program requires tampering detection to work, it might fail in Ada
2022. Needless to say, this shouldn't happen outside of test programs.
See Inconsistencies With Ada 2012 in
A.18.2
for more details.
Incompatibilities With Ada 2012
{
AI12-0111-1}
{
AI12-0112-1}
A number of new subprograms, types, and even a nested
package were added to Containers.Multiway_Trees to better support contracts
and stable views. Therefore, a use clause conflict is possible; see the
introduction of
Annex A for more on this topic.
Extensions to Ada 2012
{
AI12-0196-1}
Correction: Replace_Element is now defined
such that it can be used concurrently so long as it operates on different
elements. This allows some container operations to be used in parallel
without separate synchronization.
{
AI12-0266-1}
Most iterators can now return parallel iterators, to be used in parallel
constructs.
Wording Changes from Ada 2012
{
AI12-0069-1}
Corrigendum: Fixed the function Iterate so it is clear that the
root node is never visited.
{
AI12-0078-1}
Corrigendum: The definition of
node is clarified so that
it it doesn't appear to say all nodes have an element.
{
AI12-0110-1}
Corrigendum: Clarified that tampering checks precede all other
checks made by a subprogram (but come after those associated with the
call).
{
AI12-0112-1}
Added contracts to this container. This includes describing some of the
semantics with pre- and postconditions, rather than English text. Note
that the preconditions can be Suppressed (see
11.5).
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
