The Package Strings.Maps
Author: JTC1/SC22/WG9/ARG, by Randall Brukardt, ARG Editor

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# 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

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The library package Strings.Maps has the following declaration:
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package Ada.Strings.Maps is
pragma Pure(Maps);
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-- Representation for a set of character values:
type Character_Set is private;
pragma Preelaborable_Initialization(Character_Set);
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Null_Set : constant Character_Set;
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type Character_Range is
record
Low : Character;
High : Character;
end record;
-- Represents Character range Low..High
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type Character_Ranges is array (Positive range <>) of Character_Range;
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function To_Set (Ranges : in Character_Ranges)return Character_Set;
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function To_Set (Span : in Character_Range)return Character_Set;
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function To_Ranges (Set : in Character_Set) return Character_Ranges;
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function "=" (Left, Right : in Character_Set) return Boolean;
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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;
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function Is_In (Element : in Character;
Set : in Character_Set)
return Boolean;
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function Is_Subset (Elements : in Character_Set;
Set : in Character_Set)
return Boolean;
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function "<=" (Left : in Character_Set;
Right : in Character_Set)
return Boolean renames Is_Subset;
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-- Alternative representation for a set of character values:
subtype Character_Sequence is String;
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function To_Set (Sequence : in Character_Sequence)return Character_Set;
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function To_Set (Singleton : in Character) return Character_Set;
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function To_Sequence (Set : in Character_Set) return Character_Sequence;
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-- Representation for a character to character mapping:
type Character_Mapping is private;
pragma Preelaborable_Initialization(Character_Mapping);
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function Value (Map : in Character_Mapping;
Element : in Character)
return Character;
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Identity : constant Character_Mapping;
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function To_Mapping (From, To : in Character_Sequence)
return Character_Mapping;
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function To_Domain (Map : in Character_Mapping)
return Character_Sequence;
function To_Range (Map : in Character_Mapping)
return Character_Sequence;
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type Character_Mapping_Function is
access function (From : in Character) return Character;
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private
... -- not specified by the language
end Ada.Strings.Maps;
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An object of type Character_Set represents a set of characters.
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Null_Set represents the set containing no characters.
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An object Obj of type Character_Range represents the set of characters in the range Obj.Low .. Obj.High.
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An object Obj of type Character_Ranges represents the union of the sets corresponding to Obj(I) for I in Obj'Range.
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function To_Set (Ranges : in Character_Ranges) return Character_Set;
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If Ranges'Length=0 then Null_Set is returned; otherwise, the returned value represents the set corresponding to Ranges.
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function To_Set (Span : in Character_Range) return Character_Set;
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The returned value represents the set containing each character in Span.
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function To_Ranges (Set : in Character_Set) return Character_Ranges;
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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.
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function "=" (Left, Right : in Character_Set) return Boolean;
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The function "=" returns True if Left and Right represent identical sets, and False otherwise.
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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)).
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function Is_In (Element : in Character;
Set : in Character_Set);
return Boolean;
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Is_In returns True if Element is in Set, and False otherwise.
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function Is_Subset (Elements : in Character_Set;
Set : in Character_Set)
return Boolean;
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Is_Subset returns True if Elements is a subset of Set, and False otherwise.
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subtype Character_Sequence is String;
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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.
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function To_Set (Sequence : in Character_Sequence) return Character_Set;
function To_Set (Singleton : in Character) return Character_Set;
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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.
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function To_Sequence (Set : in Character_Set) return Character_Sequence;
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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.
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type Character_Mapping is private;
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An object of type Character_Mapping represents a Character-to-Character mapping.
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function Value (Map : in Character_Mapping;
Element : in Character)
return Character;
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The function Value returns the Character value to which Element maps with respect to the mapping represented by Map.
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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.
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String handling subprograms that deal with character mappings have parameters whose type is Character_Mapping.
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Identity : constant Character_Mapping;
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Identity maps each Character to itself.
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function To_Mapping (From, To : in Character_Sequence)
return Character_Mapping;
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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.
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function To_Domain (Map : in Character_Mapping) return Character_Sequence;
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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.
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function To_Range (Map : in Character_Mapping) return Character_Sequence;
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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.
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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
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10 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.
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11 To_Domain(Identity) and To_Range(Identity) each returns the null string.

#### Examples

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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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