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 A.18.23 The Generic Package Containers.Bounded_Hashed_Sets

{AI05-0001-1} The language-defined generic package Containers.Bounded_Hashed_Sets provides a private type Set and a set of operations. It provides the same operations as the package Containers.Hashed_Sets (see A.18.8), with the difference that the maximum storage is bounded.

Static Semantics

{AI05-0001-1} The declaration of the generic library package Containers.Bounded_Hashed_Sets has the same contents and semantics as Containers.Hashed_Sets except:
The pragma Preelaborate is replaced with pragma Pure.
The type Set 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: 
  type Set (Capacity : Count_Type;
            Modulus  : Hash_Type) is tagged private;
The type Set needs finalization if and only if type Element_Type needs finalization.
Implementation Note: {AI05-0212-1} The type Set 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. 
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. 
An additional operation is added immediately following Reserve_Capacity:
  function Default_Modulus (Capacity : Count_Type) return Hash_Type;
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).
The function Copy is replaced with: 
  function Copy (Source : Set;
                 Capacity : Count_Type := 0;
                 Modulus  : Hash_Type := 0) return Set;
{AI05-0264-1} Returns a set whose elements are initialized from the values in Source. If Capacity is 0, then the set capacity is the length of Source; if Capacity is equal to or greater than the length of Source, the set capacity is the value of the Capacity parameter; otherwise, the operation propagates Capacity_Error. If the Modulus argument is 0, then the set modulus is the value returned by a call to Default_Modulus with the set capacity as its argument; otherwise, the set modulus is the value of the Modulus parameter. 

Bounded (Run-Time) Errors

 {AI05-0160-1} {AI05-0265-1} It is a bounded error to use a bounded set 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

 {AI05-0184-1} {AI05-0264-1} For each instance of Containers.Hashed_Sets and each instance of Containers.Bounded_Hashed_Sets, if the two instances meet the following conditions, then the output generated by the Set'Output or Set'Write subprograms of either instance shall be readable by the Set'Input or Set'Read of the other instance, respectively:
{AI05-0184-1} {AI05-0248-1} the Element_Type parameters of the two instances are statically matching subtypes of the same type; and
{AI05-0184-1} 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

 {AI05-0001-1} Bounded set objects should be implemented without implicit pointers or dynamic allocation. 
Implementation Advice: Bounded set objects should be implemented without implicit pointers or dynamic allocation.
 {AI05-0001-1} 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 sets.

Extensions to Ada 2005

{AI05-0001-1} {AI05-0160-1} {AI05-0184-1} The generic package Containers.Bounded_Hashed_Sets is new. 

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