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 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 type List needs finalization if and only if
type Element_Type needs finalization.
The allocation of internal storage includes a check
that the capacity is not exceeded, and Capacity_Error is raised if this
check fails.
In procedure Assign, if Source length is greater
than Target capacity, then Capacity_Error is propagated.
The function Copy
is replaced with:
function Copy (Source : List; Capacity : Count_Type := 0)
return List;
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.
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.
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
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
