A.18.20 The Generic Package Containers.Bounded_Doubly_Linked_Lists
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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
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The declaration of the generic library package
Containers.Bounded_Doubly_Linked_Lists has the same contents and semantics
as Containers.Doubly_Linked_Lists except:3/3
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The
type List is declared with a discriminant that specifies the capacity
(maximum number of elements) as follows:
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type List (Capacity : Count_Type) is tagged private;
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The type List needs finalization
if and only if type Element_Type needs finalization.
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Implementation Note:
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The type List cannot depend on package Ada.Finalization
unless the element type depends on that package. The objects returned
from the Iterator and Reference functions probably do depend on package
Ada.Finalization. Restricted environments may need to avoid use of those
functions and their associated types.
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The allocation of internal
storage includes a check that the capacity is not exceeded, and Capacity_Error
is raised if this check fails.
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In procedure Assign, if Source
length is greater than Target capacity, then Capacity_Error is propagated.
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The
function Copy is replaced with:
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function Copy (Source : List; Capacity : Count_Type := 0)
return List;
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If Capacity is 0, then the
list capacity is the length of Source; if Capacity is equal to or greater
than the length of Source, the list capacity equals the value of the
Capacity parameter; otherwise, the operation propagates Capacity_Error.
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In the three-parameter procedure
Splice whose Source has type List, if the sum of the length of Target
and the length of Source is greater than the capacity of Target, then
Splice propagates Capacity_Error.
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In the four-parameter procedure
Splice, if the length of Target equals the capacity of Target, then Splice
propagates Capacity_Error.
Bounded (Run-Time) Errors
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It is a bounded error to use
a bounded list if it was the target of an assignment_statement
whose source was in the middle of an operation that prohibits tampering
with elements [or cursors]. Either Program_Error is raised, or the operation
proceeds as defined. Implementation Requirements
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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:16/3
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the Element_Type parameters of the two instances
are statically matching subtypes of the same type; and17/3
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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
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Bounded list objects should be implemented without
implicit pointers or dynamic allocation. 18.a.1/3
Implementation Advice:
Bounded list objects should be implemented
without implicit pointers or dynamic allocation.
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The implementation advice for procedure Move to
minimize copying does not apply. 19.a.1/3
Implementation Advice:
The implementation advice for procedure
Move to minimize copying does not apply to bounded lists.
Extensions to Ada 2005
19.a/3
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
