Re: user-defined types and basic_string

[Benjamin Kosnik <bkoz at redhat dot com>]

For archival purposes.... I find the aggregate syntax pretty awkward,
but seemingly there is no way around this, due to limits on specializing
namespace std:: types with builtins.

With Gaby's changes:

#include <string>
#include <locale>

template<typename T>
  struct character
  {
    typedef T 	value_type;
    value_type 	value;
  };

template<typename T>
  inline bool 
  operator==(character<T> lhs, character<T> rhs)
  { return lhs.value == rhs.value; }

template<typename T>
  inline bool 
  operator<(character<T> lhs, character<T> rhs)
  { return lhs.value < rhs.value; }

// Provide std::char_traits specialization.
namespace std
{
  template<typename T>
    struct char_traits<character<T> >
    {
      typedef character<T> 	 char_type;

      // NB: this type should be bigger than char_type, so as to
      // properly hold EOF values in addition to the full range of
      // char_type values.
      typedef int  		int_type;

      typedef streampos 	pos_type;
      typedef streamoff 	off_type;
      typedef mbstate_t 	state_type;
      
      static void 
      assign(char_type& __c1, const char_type& __c2)
      { __c1 = __c2; }

      static bool 
      eq(const char_type& __c1, const char_type& __c2)
      { return __c1 == __c2; }

      static bool 
      lt(const char_type& __c1, const char_type& __c2)
      { return __c1 < __c2; }

      static int 
      compare(const char_type* __s1, const char_type* __s2, size_t __n)
      { 
	for (size_t __i = 0; __i < __n; ++__i)
	  if (!eq(__s1[__i], __s2[__i]))
	    return lt(__s1[__i], __s2[__i]) ? -1 : 1;
	return 0; 
      }

      static size_t
      length(const char_type* __s)
      { 
	const char_type* __p = __s; 
	while (*__p) ++__p; 
	return (__p - __s); 
      }

      static const char_type* 
      find(const char_type* __s, size_t __n, const char_type& __a)
      { 
	for (const char_type* __p = __s; size_t(__p - __s) < __n; ++__p)
	  if (*__p == __a) return __p;
	return 0;
      }

      static char_type* 
      move(char_type* __s1, const char_type* __s2, size_t __n)
      { return (char_type*) memmove(__s1, __s2, __n * sizeof(char_type)); }

      static char_type* 
      copy(char_type* __s1, const char_type* __s2, size_t __n)
      { return (char_type*) memcpy(__s1, __s2, __n * sizeof(char_type)); }

      static char_type* 
      assign(char_type* __s, size_t __n, char_type __a)
      { 
	for (char_type* __p = __s; __p < __s + __n; ++__p) 
	  assign(*__p, __a);
        return __s; 
      }

      static char_type 
      to_char_type(const int_type& __c)
      {
	char_type __r = { __c };
	return __r;
      }

      static int_type 
      to_int_type(const char_type& __c) 
      { return int_type(__c.value); }

      static bool 
      eq_int_type(const int_type& __c1, const int_type& __c2)
      { return __c1 == __c2; }

      static int_type 
      eof() { return static_cast<int_type>(-1); }

      static int_type 
      not_eof(const int_type& __c)
      { return eq_int_type(__c, eof()) ? int_type(0) : __c; }
    };
};

int main()
{
  using namespace std;

  typedef unsigned short		value_type;
  typedef character<value_type> 	char_type;
  typedef char_traits<char_type> 	traits_type;

  bool test = true;

  // 1 char_type <-> value_type conversions
  value_type uc1 = 'c';
  value_type uc2 = 'd';
  char_type c1 = { uc1 };
  char_type c2 = { uc2 };
  test = !(c1 == c2);

  // 2 char_traits
  test = traits_type::eq(c1, c2);
  
  // 3 basic_string<char_type>
  typedef basic_string<char_type>	string_type;
  string_type str;
  char_type c3 = { value_type('b') };
  char_type c4 = { value_type('o') };
  char_type c5 = { value_type('r') };
  char_type c6 = { value_type('a') };
  char_type c7 = { value_type('c') };
  char_type c8 = { value_type('a') };
  char_type c9 = { value_type('y') };
  str += c3;
  str += c4;
  str += c5;
  str += c6;
  str += c7;
  str += c8;
  str += c9;
  string_type::size_type len = str.size();
  const char_type* arr = str.c_str();

  return 0;
}