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A.18.20 The Generic Package Containers.Bounded_Doubly_Linked_Lists

1/3
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

2/3
The declaration of the generic library package Containers.Bounded_Doubly_Linked_Lists has the same contents and semantics as Containers.Doubly_Linked_Lists except:
3/5
The aspect Preelaborate is replaced with aspect Pure.
4/3
The type List is declared with a discriminant that specifies the capacity (maximum number of elements) as follows: 
5/5
  type List (Capacity : Count_Type) is tagged private...
6/3
The type List needs finalization if and only if type Element_Type needs finalization.
6.1/5
The function Empty is replaced by:
6.2/5
   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;
7/5
For procedures Insert, Prepend, Append, Merge, and the three-parameter Splice whose parameter Source has type List, the part of the precondition reading:
7.1/5
     (<some length> <= Count_Type'Last - <some other length>
         or else raise Constraint_Error)
7.2/5
is replaced by:
7.3/5
     (<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)
8/5
In procedure Assign, the precondition is altered to: 
8.1/5
   Pre => (not Tampering_With_Cursors_Prohibited (Target)
              or else raise Program_Error) and then
           (Length (Source) <= Target.Capacity
              or else raise Capacity_Error),
9/3
The function Copy is replaced with: 
10/5
  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);
11/5
Returns a list whose elements have the same values as the elements of Source.. 
12/5
This paragraph was deleted.
13/5
In the four-parameter procedure Splice, the precondition is altered to: 
13.1/5
   Pre  => (if Tampering_With_Cursors_Prohibited (Target)
              then raise Program_Error
            elsif Tampering_With_Cursors_Prohibited (Source)
               then raise Program_Error
            elsif Position = No_Element
               then raise Constraint_Error
            elsif not Has_Element (Source, Position)
               then raise Program_Error
            elsif Before /= No_Element and then
               not Has_Element (Target, Before)
               then raise Program_Error
            elsif Same_Object (Target, Source) then True
            elsif Length (Target) = Count_Type'Last
              then raise Constraint_Error
            elsif Length (Target) = Target.Capacity
              then raise Capacity_Error),

Bounded (Run-Time) Errors

14/3
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

15/3
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

16/3
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:
17/3
the Element_Type parameters of the two instances are statically matching subtypes of the same type; and
18/3
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

19/3
Bounded list objects should be implemented without implicit pointers or dynamic allocation. 
20/3
The implementation advice for procedure Move to minimize copying does not apply. 

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