A.18.19 The Generic Package Containers.Bounded_Vectors
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The language-defined generic package Containers.Bounded_Vectors
provides a private type Vector and a set of operations. It provides the
same operations as the package Containers.Vectors (see A.18.2),
with the difference that the maximum storage is bounded.Static Semantics
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The declaration of the generic library package
Containers.Bounded_Vectors has the same contents and semantics as Containers.Vectors
except:The
type Vector is declared with a discriminant that specifies the capacity:
type Vector (Capacity : Count_Type) is tagged private;
The type Vector needs finalization
if and only if type Element_Type needs finalization.
Implementation Note:
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The type Vector 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.
In function Copy, if the
Capacity parameter is equal to or greater than the length of Source,
the vector capacity exactly equals the value of the Capacity parameter.
The
description of Reserve_Capacity is replaced with:
If the specified Capacity
is larger than the capacity of Container, then Reserve_Capacity propagates
Capacity_Error. Otherwise, the operation has no effect.
Bounded (Run-Time) Errors
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It is a bounded error to assign
from a bounded vector 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. Proof: Tampering
with elements includes tampering with cursors, so we only really need
to talk about tampering with elements here; we mention cursors for clarity.
Erroneous Execution
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When a bounded vector object V is finalized,
if tampering with cursors is prohibited for V other than due to
an assignment from another vector, then execution is erroneous. Reason: This is
a tampering event, but since the implementation is not allowed to use
Ada.Finalization, it is not possible in a pure Ada implementation to
detect this error. (There is no Finalize routine that will be called
that could make the check.) Since the check probably cannot be made,
the bad effects that could occur (such as an iterator going into an infinite
loop or accessing a nonexistent element) cannot be prevented and we have
to allow anything. We do allow re-assigning an object that only prohibits
tampering because it was copied from another object as that cannot cause
any negative effects.
Implementation Requirements
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For each instance of Containers.Vectors and each
instance of Containers.Bounded_Vectors, if the two instances meet the
following conditions, then the output generated by the Vector'Output
or Vector'Write subprograms of either instance shall be readable by the
Vector'Input or Vector'Read of the other instance, respectively:{
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the Element_Type parameters of the two instances
are statically matching subtypes of the same type; and{
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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); and{
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the preceding two conditions also hold for the
Index_Type parameters of the instances. Implementation Advice
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Bounded vector objects should be implemented without
implicit pointers or dynamic allocation. Implementation Advice:
Bounded vector 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. Implementation Advice:
The implementation advice for procedure
Move to minimize copying does not apply to bounded vectors.
Extensions to Ada 2005
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
