Ada Reference Manual (Ada 2022)
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...
- The aspect_definition for Preelaborable_Initialization for type List is changed to:
Preelaborable_Initialization =>
Element_Type'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;
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)
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)
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),
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);
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),
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.
