A.18.21 The Generic Package Containers.Bounded_Hashed_Maps
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The language-defined generic package Containers.Bounded_Hashed_Maps
provides a private type Map and a set of operations. It provides the
same operations as the package Containers.Hashed_Maps (see A.18.5),
with the difference that the maximum storage is bounded.Static Semantics
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The declaration of the generic library package
Containers.Bounded_Hashed_Maps has the same contents and semantics as
Containers.Hashed_Maps except:3/3
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The
type Map is declared with discriminants that specify both the capacity
(number of elements) and modulus (number of distinct hash values) of
the hash table as follows:
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type Map (Capacity : Count_Type;
Modulus : Hash_Type) is tagged private;
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The type Map needs finalization
if and only if type Key_Type or type Element_Type needs finalization.
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Implementation Note:
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The type Map cannot depend on package Ada.Finalization
unless the element or key 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
description of Reserve_Capacity is replaced with:
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If the specified Capacity
is larger than the capacity of Container, then Reserve_Capacity propagates
Capacity_Error. Otherwise, the operation has no effect.
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An
additional operation is added immediately following Reserve_Capacity:
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function Default_Modulus (Capacity : Count_Type) return Hash_Type;
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Default_Modulus returns
an implementation-defined value for the number of distinct hash values
to be used for the given capacity (maximum number of elements).
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The
function Copy is replaced with:
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function Copy (Source : Map;
Capacity : Count_Type := 0;
Modulus : Hash_Type := 0) return Map;
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Returns a map with key/element pairs initialized
from the values in Source. If Capacity is 0, then the map capacity is
the length of Source; if Capacity is equal to or greater than the length
of Source, the map capacity is the value of the Capacity parameter; otherwise,
the operation propagates Capacity_Error. If the Modulus argument is
0, then the map modulus is the value returned by a call to Default_Modulus
with the map capacity as its argument; otherwise, the map modulus is
the value of the Modulus parameter. Bounded (Run-Time) Errors
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It is a bounded error to use
a bounded map 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.Hashed_Maps and
each instance of Containers.Bounded_Hashed_Maps, if the two instances
meet the following conditions, then the output generated by the Map'Output
or Map'Write subprograms of either instance shall be readable by the
Map'Input or Map'Read of the other instance, respectively:17/3
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the Element_Type parameters of the two instances
are statically matching subtypes of the same type; and18/3
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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); and19/3
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the preceding two conditions also hold for the
Key_Type parameters of the instances. Implementation Advice
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Bounded map objects should be implemented without
implicit pointers or dynamic allocation. 20.a.1/3
Implementation Advice:
Bounded map 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. 21.a.1/3
Implementation Advice:
The implementation advice for procedure
Move to minimize copying does not apply to bounded maps.
Extensions to Ada 2005
21.a/3
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
