A.18.12 The Generic Package Containers.Indefinite_Doubly_Linked_Lists
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The language-defined generic package Containers.Indefinite_Doubly_Linked_Lists
provides private types List and Cursor, and a set of operations for each
type. It provides the same operations as the package Containers.Doubly_Linked_Lists
(see
A.18.3), with the difference that the
generic formal Element_Type is indefinite.
Static Semantics
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The declaration of the generic library package Containers.Indefinite_Doubly_Linked_Lists
has the same contents and semantics as Containers.Doubly_Linked_Lists
except:
The generic formal Element_Type is indefinite.
The procedure with
the profile:
procedure Insert (Container : in out List;
Before : in Cursor;
Position : out Cursor;
Count : in Count_Type := 1);
is omitted.
Discussion: This procedure is omitted
because there is no way to create a default-initialized object of an
indefinite type. We considered having this routine insert an empty element
similar to the empty elements of a vector, but rejected this possibility
because the semantics are fairly complex and very different from the
existing definite container. That would make it more error-prone to convert
a container from a definite type to an indefinite type; by omitting the
routine completely, any problems will be diagnosed by the compiler.
The actual Element parameter of access subprogram
Process of Update_Element may be constrained even if Element_Type is
unconstrained.
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The operations Append, Insert, Prepend, and Replace_Element that have
a formal parameter of type Element_Type perform indefinite insertion
(see
A.18).
Extensions to Ada 95
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The generic package Containers.Indefinite_Doubly_Linked_Lists
is new.
Inconsistencies With Ada 2012
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Corrigendum: Defined some routines to “perform
indefinite insertion”. This could mean that some calls to those
routines would now raise Program_Error where they previously worked.
However, this is extremely unlikely; see Inconsistencies With Ada 2012
in
A.18.11 for details.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
