A.18.25 The Generic Package Containers.Bounded_Multiway_Trees
The language-defined generic package Containers.Bounded_Multiway_Trees
provides a private type Tree and a set of operations. It provides the
same operations as the package Containers.Multiway_Trees (see
A.18.10),
with the difference that the maximum storage is bounded.
Static Semantics
The declaration of
the generic library package Containers.Bounded_Multiway_Trees has the
same contents and semantics as Containers.Multiway_Trees except:
The type Tree is
declared with a discriminant that specifies the capacity (maximum number
of elements) as follows:
type Tree (Capacity : Count_Type) is tagged private;
The type Tree needs finalization if and only if
type Element_Type needs finalization.
The allocation of internal storage includes a check
that the capacity is not exceeded, and Capacity_Error is raised if this
check fails.
In procedure Assign, if Source length is greater
than Target capacity, then Capacity_Error is propagated.
Function Copy is
declared as follows:
function Copy (Source : Tree; Capacity : Count_Type := 0)
return Tree;
If Capacity is 0, then the tree capacity
is the count of Source; if Capacity is equal to or greater than Source.Count,
the tree capacity equals the value of the Capacity parameter; otherwise,
the operation propagates Capacity_Error.
In the five-parameter procedure Splice_Subtree,
if Source is not the same object as Target, and if the sum of Target.Count
and Subtree_Node_Count (Position) is greater than Target.Capacity, then
Splice_Subtree propagates Capacity_Error.
In the five-parameter procedure Splice_Children,
if Source is not the same object as Target, and if the sum of Target.Count
and Subtree_Node_Count (Source_Parent)-1 is greater than Target.Capacity,
then Splice_Children propagates Capacity_Error.
Bounded (Run-Time) Errors
It is a bounded error to assign
from a bounded tree object while tampering with elements or cursors of
that object is prohibited. Either Program_Error is raised by the assignment,
execution proceeds with the target object prohibiting tampering with
elements or cursors, or execution proceeds normally.
Erroneous Execution
When a bounded tree object
T is finalized,
if tampering with cursors is prohibited for
T other than due to
an assignment from another tree, then execution is erroneous.
Implementation Requirements
For each instance
of Containers.Multiway_Trees and each instance of Containers.Bounded_Multiway_Trees,
if the two instances meet the following conditions, then the output generated
by the Tree'Output or Tree'Write subprograms of either instance shall
be readable by the Tree'Input or Tree'Read of the other instance, respectively:
the Element_Type parameters of the two instances
are statically matching subtypes of the same type; and
the output generated by Element_Type'Output or
Element_Type'Write is readable by Element_Type'Input or Element_Type'Read,
respectively (where Element_Type denotes the type of the two actual Element_Type
parameters).
Implementation Advice
Bounded tree objects should be implemented without
implicit pointers or dynamic allocation.
The implementation advice for procedure Move to
minimize copying does not apply.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
