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 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.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
