A.18.20 The Generic Package Containers.Bounded_Doubly_Linked_Lists
The language-defined generic package Containers.Bounded_Doubly_Linked_Lists
provides a private type List and a set of operations. It provides the
same operations as the package Containers.Doubly_Linked_Lists (see
A.18.3),
with the difference that the maximum storage is bounded.
Static Semantics
The declaration of
the generic library package Containers.Bounded_Doubly_Linked_Lists has
the same contents and semantics as Containers.Doubly_Linked_Lists except:
The aspect Preelaborate is replaced with aspect
Pure. Aspect Global is deleted.
The type List is
declared with a discriminant that specifies the capacity (maximum number
of elements) as follows:
type List (Capacity : Count_Type) is tagged private...
Preelaborable_Initialization =>
Element_Type'Preelaborable_Initialization
The type List needs finalization if and only if
type Element_Type needs finalization.
The function Empty
is replaced by:
function Empty (Capacity : Count_Type := implementation-defined)
return List
with Post =>
Empty'Result.Capacity = Capacity and then
not Tampering_With_Elements_Prohibited (Empty'Result) and then
not Tampering_With_Cursors_Prohibited (Empty'Result) and then
Length (Empty'Result) = 0;
For procedures Insert, Prepend, Append, Merge,
and the three-parameter Splice whose parameter Source has type List,
the part of the precondition reading:
(<some length> <= Count_Type'Last - <some other length>
or else raise Constraint_Error)
is replaced
by:
(<some length> <= Count_Type'Last - <some other length>
or else raise Constraint_Error) and then
(<some length> <= Container.Capacity - <some other length>
or else raise Capacity_Error)
In procedure Assign, the precondition is altered
to:
Pre => (not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error) and then
(Length (Source) <= Target.Capacity
or else raise Capacity_Error),
The function Copy
is replaced with:
function Copy (Source : List; Capacity : Count_Type := 0)
return List
with Pre => Capacity = 0
or else Capacity >= Length (Source)
or else raise Capacity_Error,
Post =>
Length (Copy'Result) = Length (Source)
and then
not Tampering_With_Elements_Prohibited (Copy'Result)
and then
not Tampering_With_Cursors_Prohibited (Copy'Result)
and then
Copy'Result.Capacity = (
if Capacity = 0
then
Length (Source)
else Capacity);
Returns a list whose elements have the same values
as the elements of Source.
This paragraph
was deleted.
In the four-parameter procedure Splice, the precondition
is altered to:
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
(Position /= No_Element
or else raise Constraint_Error) and then
(Has_Element (Source, Position)
or else raise Program_Error) and then
(Before = No_Element or else Has_Element (Target, Before)
or else raise Program_Error) and then
(Target'Has_Same_Storage (Source) or else
Length (Target) /= Count_Type'Last
or else raise Constraint_Error) and then
(Target'Has_Same_Storage (Source) or else
Length (Target) /= Target.Capacity
or else raise Capacity_Error),
Bounded (Run-Time) Errors
It is a bounded error to assign
from a bounded list 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 list object
L is finalized,
if tampering with cursors is prohibited for
L other than due to
an assignment from another list, then execution is erroneous.
Implementation Requirements
For each instance of
Containers.Doubly_Linked_Lists and each instance of Containers.Bounded_Doubly_Linked_Lists,
if the two instances meet the following conditions, then the output generated
by the List'Output or List'Write subprograms of either instance shall
be readable by the List'Input or List'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 list 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
