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A.4.2 The Package Strings.Maps

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

    Static Semantics

  2. The library package Strings.Maps has the following declaration:
  3. package Ada.Strings.Maps is
       pragma Preelaborate(Maps);
    
  4.    -- Representation for a set of character values:
       type Character_Set is private;
    
  5.    Null_Set : constant Character_Set;
    
  6.    type Character_Range is
         record
            Low  : Character;
            High : Character;
         end record;
       -- Represents Character range Low..High
    
  7.    type Character_Ranges is
         array (Positive range <>) of Character_Range;
    
  8.    function To_Set (Ranges : in Character_Ranges)
         return Character_Set;
    
  9.    function To_Set (Span : in Character_Range)
         return Character_Set;
    
  10.    function To_Ranges (Set : in Character_Set)
         return Character_Ranges;
    
  11.    function "=" (Left, Right : in Character_Set) return Boolean;
    
  12.    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;
    
  13.    function Is_In (Element : in Character;
                       Set     : in Character_Set)
          return Boolean;
    
  14.    function Is_Subset (Elements : in Character_Set;
                           Set      : in Character_Set)
          return Boolean;
    
  15.    function "<=" (Left  : in Character_Set;
                      Right : in Character_Set)
          return Boolean renames Is_Subset;
    
  16.    -- Alternative representation for a set of character values:
       subtype Character_Sequence is String;
    
  17.    function To_Set (Sequence : in Character_Sequence)
         return Character_Set;
    
  18.    function To_Set (Singleton : in Character) return Character_Set;
    
  19.    function To_Sequence (Set : in Character_Set)
         return Character_Sequence;
    
  20.    -- Representation for a character to character mapping:
       type Character_Mapping is private;
    
  21.    function Value (Map     : in Character_Mapping;
                       Element : in Character)
          return Character;
    
  22.    Identity : constant Character_Mapping;
    
  23.    function To_Mapping (From, To : in Character_Sequence)
         return Character_Mapping;
    
  24.    function To_Domain (Map : in Character_Mapping)
         return Character_Sequence;
       function To_Range  (Map : in Character_Mapping)
         return Character_Sequence;
    
  25.    type Character_Mapping_Function is
          access function (From : in Character) return Character;
    
  26. private
       ... -- not specified by the language
    end Ada.Strings.Maps;
    
  27. An object of type Character_Set represents a set of characters.
  28. Null_Set represents the set containing no characters.
  29. An object Obj of type Character_Range represents the set of characters in the range Obj.Low .. Obj.High.
  30. An object Obj of type Character_Ranges represents the union of the sets corresponding to Obj(I) for I in Obj'Range.
  31. function To_Set (Ranges : in Character_Ranges) return Character_Set;
    
    1. If Ranges'Length=0 then Null_Set is returned; otherwise the returned value represents the set corresponding to Ranges.

  1. function To_Set (Span : in Character_Range) return Character_Set;
    
    1. The returned value represents the set containing each character in Span.

  1. function To_Ranges (Set : in Character_Set) return Character_Ranges;
    
    1. 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.

  1. function "=" (Left, Right : in Character_Set) return Boolean;
    
    1. The function "=" returns True if Left and Right represent identical sets, and False otherwise.

  1. 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)).
  2. function Is_In (Element : in Character;
                    Set     : in Character_Set);
       return Boolean;
    
    1. Is_In returns True if Element is in Set, and False otherwise.

  1. function Is_Subset (Elements : in Character_Set;
                        Set      : in Character_Set)
       return Boolean;
    
    1. Is_Subset returns True if Elements is a subset of Set, and False otherwise.

  1. subtype Character_Sequence is String;
    
    1. 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.

  1. function To_Set (Sequence  : in Character_Sequence)
      return Character_Set;
    
    function To_Set (Singleton : in Character)
      return Character_Set;
    
    1. 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.

  1. function To_Sequence (Set : in Character_Set)
      return Character_Sequence;
    
    1. 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.

  1. type Character_Mapping is private;
    
    1. An object of type Character_Mapping represents a Character-to-Character mapping.

  1. function Value (Map     : in Character_Mapping;
                    Element : in Character)
       return Character;
    
    1. The function Value returns the Character value to which Element maps with respect to the mapping represented by Map.

  1. 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.
  2. String handling subprograms that deal with character mappings have parameters whose type is Character_Mapping.
  3. Identity : constant Character_Mapping;
    
    1. Identity maps each Character to itself.

  1. function To_Mapping (From, To : in Character_Sequence)
      return Character_Mapping;
    
    1. 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.

  1. function To_Domain (Map : in Character_Mapping)
      return Character_Sequence;
    
    1. 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.

  1. function To_Range (Map : in Character_Mapping)
      return Character_Sequence;
    
    1. To_Range returns the Character_Sequence value R, with lower bound 1 and upper bound Map'Length, such that if D = To_Domain(Map) then D(I) maps to R(I) for each I in D'Range.

  1. 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.

    NOTES

  2. (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.
  3. (8) To_Domain(Identity) and To_Range(Identity) each returns the null string.

    Examples

  4. 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.


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