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## Struct template null_regex_traits

boost::xpressive::null_regex_traits — stub regex_traits for non-char data

## Synopsis

    // In header: <boost/xpressive/xpressive_fwd.hpp>

    template<typename Elem>
    struct null_regex_traits {

      // public member functions
      null_regex_traits(locale_type = locale_type());
      bool operator==(null_regex_traits< char_type > const &) const;
      bool operator!=(null_regex_traits< char_type > const &) const;
      char_type widen(char) const;

      // public static functions
      static unsigned char hash(char_type);
      static char_type translate(char_type);
      static char_type translate_nocase(char_type);
      static bool in_range(char_type, char_type, char_type);
      static bool in_range_nocase(char_type, char_type, char_type);
      template<typename FwdIter> static string_type transform(FwdIter, FwdIter);
      template<typename FwdIter>
        static string_type transform_primary(FwdIter, FwdIter);
      template<typename FwdIter>
        static string_type lookup_collatename(FwdIter, FwdIter);
      template<typename FwdIter>
        static char_class_type lookup_classname(FwdIter, FwdIter, bool);
      static bool isctype(char_type, char_class_type);
      static int value(char_type, int);
      static locale_type imbue(locale_type);
      static locale_type getloc();
    };

## Description

### `null_regex_traits` public member functions

1.     null_regex_traits(locale_type = locale_type());

   Initialize a null_regex_traits object.

2.     bool operator==(null_regex_traits< char_type > const & that) const;

   Checks two null_regex_traits objects for equality

   Returns: | true.

3.     bool operator!=(null_regex_traits< char_type > const & that) const;

   Checks two null_regex_traits objects for inequality

   Returns: | false.

4.     char_type widen(char ch) const;

   Convert a char to a Elem

   Parameters: |
   `ch` | The source character.
   Returns: | Elem(ch).

### `null_regex_traits` public static functions

1.     static unsigned char hash(char_type ch);

   Returns a hash value for a Elem in the range [0, UCHAR_MAX]

   Parameters: |
   `ch` | The source character.
   Returns: | a value between 0 and UCHAR_MAX, inclusive.

2.     static char_type translate(char_type ch);

   No-op

   Parameters: |
   `ch` | The source character.
   Returns: | ch

3.     static char_type translate_nocase(char_type ch);

   No-op

   Parameters: |
   `ch` | The source character.
   Returns: | ch

4.     static bool in_range(char_type first, char_type last, char_type ch);

   Checks to see if a character is within a character range.

   Parameters: |
   `first` | The bottom of the range, inclusive.
   `last` | The top of the range, inclusive.
   `ch` | The source character.
   Returns: | first <= ch && ch <= last.

5.     static bool in_range_nocase(char_type first, char_type last, char_type ch);

   Checks to see if a character is within a character range.

   | Important
   Since the null_regex_traits does not do case-folding, this function is equivalent to in_range().

   Parameters: |
   `first` | The bottom of the range, inclusive.
   `last` | The top of the range, inclusive.
   `ch` | The source character.
   Returns: | first <= ch && ch <= last.

6.     template<typename FwdIter>
         static string_type transform(FwdIter begin, FwdIter end);

   Returns a sort key for the character sequence designated by the iterator range [F1, F2) such that if the character sequence [G1, G2) sorts before the character sequence [H1, H2) then v.transform(G1, G2) < v.transform(H1, H2).

   | Important
   Not currently used

7.     template<typename FwdIter>
         static string_type transform_primary(FwdIter begin, FwdIter end);

   Returns a sort key for the character sequence designated by the iterator range [F1, F2) such that if the character sequence [G1, G2) sorts before the character sequence [H1, H2) when character case is not considered then v.transform_primary(G1, G2) < v.transform_primary(H1, H2).

   | Important
   Not currently used

8.     template<typename FwdIter>
         static string_type lookup_collatename(FwdIter begin, FwdIter end);

   Returns a sequence of characters that represents the collating element consisting of the character sequence designated by the iterator range [F1, F2). Returns an empty string if the character sequence is not a valid collating element.

   | Important
   Not currently used

9.     template<typename FwdIter>
         static char_class_type
         lookup_classname(FwdIter begin, FwdIter end, bool icase);

   The null_regex_traits does not have character classifications, so lookup_classname() is unused.

   Parameters: |
   `begin` | not used
   `end` | not used
   `icase` | not used
   Returns: | static_cast<char_class_type>(0)

10.     static bool isctype(char_type ch, char_class_type mask);

    The null_regex_traits does not have character classifications, so isctype() is unused.

    Parameters: |
    `ch` | not used
    `mask` | not used
    Returns: | false

11.     static int value(char_type ch, int radix);

    The null_regex_traits recognizes no elements as digits, so value() is unused.

    Parameters: |
    `ch` | not used
    `radix` | not used
    Returns: | -1

12.     static locale_type imbue(locale_type loc);

    Not used

    Parameters: |
    `loc` | not used
    Returns: | loc

13.     static locale_type getloc();

    Returns locale_type().

    Returns: | locale_type()