A.4.2 The Package Strings.Maps

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The package Strings.Maps defines the types, operations, and other entities needed for character sets and character-to-character mappings.

Static Semantics

The library package Strings.Maps has the following declaration:

package Ada.Strings.Maps is
    pragma Preelaborate(Maps);

    -- Representation for a set of character values: 
    type Character_Set is private;

    Null_Set : constant Character_Set;

    type Character_Range is
            Low  : Character;
            High : Character;
        end record;
    -- Represents Character range Low..High

    type Character_Ranges is array (Positive range <>) of Character_Range;

    function To_Set    (Ranges in Character_Ranges)return Character_Set;

    function To_Set    (Span   in Character_Range)return Character_Set;

    function To_Ranges (Set    in Character_Set)  return Character_Ranges;

    function "="   (Left, Right in Character_Set) return Boolean;

    function "not" (Right in Character_Set)       return Character_Set; 
    function "and" (Left, Right in Character_Set) return Character_Set; 
    function "or"  (Left, Right in Character_Set) return Character_Set; 
    function "xor" (Left, Right in Character_Set) return Character_Set; 
    function "-"   (Left, Right in Character_Set) return Character_Set;

    function Is_In (Element in Character;
                    Set     in Character_Set)    
        return Boolean;

    function Is_Subset (Elements in Character_Set; 
                    Set      in Character_Set)    
        return Boolean;

    function "<=" (Left  in Character_Set;
                   Right in Character_Set)    
        return Boolean renames Is_Subset;

    -- Alternative representation for a set of character values: 
    subtype Character_Sequence is String;

    function To_Set (Sequence  in Character_Sequence)return Character_Set;

    function To_Set (Singleton in Character)     return Character_Set;

    function To_Sequence (Set  in Character_Set) return Character_Sequence;

    -- Representation for a character to character mapping: 
    type Character_Mapping is private;

    function Value (Map     in Character_Mapping;
                    Element in Character)
        return Character;

    Identity : constant Character_Mapping;

    function To_Mapping (From, To in Character_Sequence)
        return Character_Mapping;

    function To_Domain (Map in Character_Mapping)
        return Character_Sequence; 
    function To_Range  (Map in Character_Mapping)
        return Character_Sequence;

    type Character_Mapping_Function is 
        access function (From in Character) return Character;

    ... -- not specified by the language
end Ada.Strings.Maps;

An object of type Character_Set represents a set of characters.

Null_Set represents the set containing no characters.

An object Obj of type Character_Range represents the set of characters in the range Obj.Low .. Obj.High.

An object Obj of type Character_Ranges represents the union of the sets corresponding to Obj(I) for I in Obj'Range.

function To_Set (Ranges in Character_Ranges) return Character_Set;

If Ranges'Length=0 then Null_Set is returned; otherwise the returned value represents the set corresponding to Ranges.

function To_Set (Span in Character_Range) return Character_Set;

The returned value represents the set containing each character in Span.

function To_Ranges (Set in Character_Set) return Character_Ranges;

If Set = Null_Set then an empty Character_Ranges array is returned; otherwise the shortest array of contiguous ranges of Character values in Set, in increasing order of Low, is returned.

function "=" (Left, Right in Character_Set) return Boolean;

The function "=" returns True if Left and Right represent identical sets, and False otherwise.

Each of the logical operators "not", "and", "or", and "xor" returns a Character_Set value that represents the set obtained by applying the corresponding operation to the set(s) represented by the parameter(s) of the operator. "-"(Left, Right) is equivalent to "and"(Left, "not"(Right)).

function Is_In (Element in Character;
                Set     in Character_Set);
    return Boolean;

Is_In returns True if Element is in Set, and False otherwise.

function Is_Subset (Elements in Character_Set; 
                    Set      in Character_Set) 
    return Boolean;

Is_Subset returns True if Elements is a subset of Set, and False otherwise.

subtype Character_Sequence is String;

The Character_Sequence subtype is used to portray a set of character values and also to identify the domain and range of a character mapping.

function To_Set (Sequence  in Character_Sequence) return Character_Set;function To_Set (Singleton in Character)          return Character_Set;

Sequence portrays the set of character values that it explicitly contains (ignoring duplicates). Singleton portrays the set comprising a single Character. Each of the To_Set functions returns a Character_Set value that represents the set portrayed by Sequence or Singleton.

function To_Sequence (Set in Character_Set) return Character_Sequence;

The function To_Sequence returns a Character_Sequence value containing each of the characters in the set represented by Set, in ascending order with no duplicates.

type Character_Mapping is private;

An object of type Character_Mapping represents a Character-to-Character mapping.

function Value (Map     in Character_Mapping;
                Element in Character)
    return Character;

The function Value returns the Character value to which Element maps with respect to the mapping represented by Map.

A character C matches a pattern character P with respect to a given Character_Mapping value Map if Value(Map, C) = P. A string S matches a pattern string P with respect to a given Character_Mapping if their lengths are the same and if each character in S matches its corresponding character in the pattern string P.

String handling subprograms that deal with character mappings have parameters whose type is Character_Mapping.

Identity : constant Character_Mapping;

Identity maps each Character to itself.

function To_Mapping (From, To in Character_Sequence)
    return Character_Mapping;

To_Mapping produces a Character_Mapping such that each element of From maps to the corresponding element of To, and each other character maps to itself. If From'Length /= To'Length, or if some character is repeated in From, then Translation_Error is propagated.

function To_Domain (Map in Character_Mapping) return Character_Sequence;

To_Domain returns the shortest Character_Sequence value D such that each character not in D maps to itself, and such that the characters in D are in ascending order. The lower bound of D is 1.

function To_Range  (Map in Character_Mapping) return Character_Sequence;

To_Range returns the Character_Sequence value R, such that if D = To_Domain(Map), then R has the same bounds as D, and D(I) maps to R(I) for each I in D'Range.

An object F of type Character_Mapping_Function maps a Character value C to the Character value F.all(C), which is said to match C with respect to mapping function F.


7  Character_Mapping and Character_Mapping_Function are used both for character equivalence mappings in the search subprograms (such as for case insensitivity) and as transformational mappings in the Translate subprograms.

8  To_Domain(Identity) and To_Range(Identity) each returns the null string.


To_Mapping("ABCD", "ZZAB") returns a Character_Mapping that maps 'A' and 'B' to 'Z', 'C' to 'A', 'D' to 'B', and each other Character to itself.

Copyright © 1992,1993,1994,1995 Intermetrics, Inc.
Copyright © 2000 The MITRE Corporation, Inc. Ada Reference Manual