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A.18.23 The Generic Package Containers.Bounded_Hashed_Sets

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

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.
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;
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

 It is a bounded error to assign from a bounded set 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 set object S is finalized, if tampering with cursors is prohibited for S other than due to an assignment from another set, then execution is erroneous.

Implementation Requirements

 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:
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 hashed set objects should be implemented without implicit pointers or dynamic allocation. 
 The implementation advice for procedure Move to minimize copying does not apply. 

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