Ada Reference Manual (Ada 2022) — Legal Information

# A.18.21 The Generic Package Containers.Bounded_Hashed_Maps

1/3
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

2/3
The declaration of the generic library package Containers.Bounded_Hashed_Maps has the same contents and semantics as Containers.Hashed_Maps except:
3/5
The aspect Preelaborate is replaced with aspect Pure. Aspect Global is deleted.
4/3
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:
5/5
type Map (Capacity : Count_Type;
Modulus : Hash_Type) is tagged private...
5.1/5
The aspect_definition for Preelaborable_Initialization for type Map is changed to:
5.2/5
Preelaborable_Initialization =>
Element_Type'Preelaborable_Initialization
and
Key_Type'Preelaborable_Initialization
6/3
The type Map needs finalization if and only if type Key_Type or type Element_Type needs finalization.
6.1/5
In function Empty, the postcondition is altered to:
6.2/5
Post =>
Empty'Result.Capacity = Capacity and then
Empty'Result.Modulus = Default_Modulus (Capacity) and then
not Tampering_With_Elements_Prohibited (Empty'Result) and then
not Tampering_With_Cursors_Prohibited (Empty'Result) and then
Length (Empty'Result) = 0;
7/3
The description of Reserve_Capacity is replaced with:
7.1/5
procedure Reserve_Capacity (Container : in out Map;
Capacity : in Count_Type)
with Pre => Capacity <= Container.Capacity
or else raise Capacity_Error;
8/5
This operation has no effect, other than checking the precondition.
9/3
An additional operation is added immediately following Reserve_Capacity:
10/3
function Default_Modulus (Capacity : Count_Type) return Hash_Type;
11/3
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).
11.1/5
For procedures Insert and Include, the part of the precondition reading:
11.2/5
(<some length> <= Count_Type'Last - <some other length>
or else raise Constraint_Error)
11.3/5
is replaced by:
11.4/5
(<some length> <= Count_Type'Last - <some other length>
or else raise Constraint_Error) and then
(<some length> > Container.Capacity - <some other length>
or else raise Capacity_Error)
11.5/5
In procedure Assign, the precondition is altered to:
11.6/5
Pre => (not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error) and then
(Length (Source) <= Target.Capacity
or else raise Capacity_Error),
12/3
The function Copy is replaced with:
13/5
function Copy (Source : Map;
Capacity : Count_Type := 0;
Modulus : Hash_Type := 0) return Map
with Pre => Capacity = 0 or else Capacity >= Length (Source)
or else raise Capacity_Error,
Post =>
Length (Copy'Result) = Length (Source) and then
not Tampering_With_Elements_Prohibited (Copy'Result) and then
not Tampering_With_Cursors_Prohibited (Copy'Result) and then
Copy'Result.Capacity = (if Capacity = 0 then
Length (Source) else Capacity) and then
Copy'Result.Modulus = (if Modulus = 0 then
Default_Modulus (Capacity) else Modulus);
14/5
Returns a map with key/element pairs initialized from the values in Source.

#### Bounded (Run-Time) Errors

15/3
It is a bounded error to assign from a bounded map 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

16/3
When a bounded map object M is finalized, if tampering with cursors is prohibited for M other than due to an assignment from another map, then execution is erroneous.

#### Implementation Requirements

17/3
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:
18/3
the Element_Type parameters of the two instances are statically matching subtypes of the same type; and
19/3
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
20/3
the preceding two conditions also hold for the Key_Type parameters of the instances.

#### Implementation Advice

21/3
Bounded hashed map objects should be implemented without implicit pointers or dynamic allocation.
22/3
The implementation advice for procedure Move to minimize copying does not apply.

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