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A.4.6 String-Handling Sets and Mappings

1
The language-defined package Strings.Maps.Constants declares Character_Set and Character_Mapping constants corresponding to classification and conversion functions in package Characters.Handling.
1.a
Discussion: The Constants package is a child of Strings.Maps since it needs visibility of the private part of Strings.Maps in order to initialize the constants in a preelaborable way (i.e. via aggregates versus function calls). 

Static Semantics

2
The library package Strings.Maps.Constants has the following declaration:
3/2
{AI95-00362-01} package Ada.Strings.Maps.Constants is
   pragma Pure Preelaborate(Constants);
4
   Control_Set           : constant Character_Set;
   Graphic_Set           : constant Character_Set;
   Letter_Set            : constant Character_Set;
   Lower_Set             : constant Character_Set;
   Upper_Set             : constant Character_Set;
   Basic_Set             : constant Character_Set;
   Decimal_Digit_Set     : constant Character_Set;
   Hexadecimal_Digit_Set : constant Character_Set;
   Alphanumeric_Set      : constant Character_Set;
   Special_Set           : constant Character_Set;
   ISO_646_Set           : constant Character_Set;
5
   Lower_Case_Map        : constant Character_Mapping;
     --Maps to lower case for letters, else identity
   Upper_Case_Map        : constant Character_Mapping;
     --Maps to upper case for letters, else identity
   Basic_Map             : constant Character_Mapping;
     --Maps to basic letter for letters, else identity
6
private
   ... -- not specified by the language
end Ada.Strings.Maps.Constants;
7
Each of these constants represents a correspondingly named set of characters or character mapping in Characters.Handling (see A.3.2). 
NOTES
8/3
15  {AI05-0114-1} There are certain characters which are defined to be lower case letters by ISO 10646 and are therefore allowed in identifiers, but are not considered lower case letters by Ada.Strings.Maps.Constants.
8.a/3
Reason: This is to maintain runtime compatibility with the Ada 95 definitions of these constants; existing correct programs could break if the definitions were changed in a way the programs did not anticipate. 

Extensions to Ada 95

8.b/2
{AI95-00362-01} Strings.Maps.Constants is now Pure, so it can be used in pure units. 

Wording Changes from Ada 2005

8.c/3
{AI05-0114-1} Correction: Added a note to clarify that these constants don't have any relationship to the characters allowed in identifiers. 

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