type7.hpp

C++ Templates 完全导引范例

/* The following code example is taken from the book
 * "C++ Templates - The Complete Guide"
 * by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
 *
 * (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
struct SizeOverOne { char c[2]; };

template<typename T,
         bool convert_possible = !CompoundT<T>::IsFuncT &&
                                 !CompoundT<T>::IsArrayT>
class ConsumeUDC {
  public:
    operator T() const;
};

// conversion to function types is not possible
template <typename T>
class ConsumeUDC<T, false> {
};

// conversion to void type is not possible
template <bool convert_possible>
class ConsumeUDC<void, convert_possible> {
};

char enum_check(bool);
char enum_check(char);
char enum_check(signed char);
char enum_check(unsigned char);
char enum_check(wchar_t);

char enum_check(signed short);
char enum_check(unsigned short);
char enum_check(signed int);
char enum_check(unsigned int);
char enum_check(signed long);
char enum_check(unsigned long);
#if LONGLONG_EXISTS
  char enum_check(signed long long);
  char enum_check(unsigned long long);
#endif  // LONGLONG_EXISTS

// avoid accidental conversions from float to int
char enum_check(float);
char enum_check(double);
char enum_check(long double);

SizeOverOne enum_check(...);    // catch all

template<typename T>
class IsEnumT {
  public:
    enum { Yes = IsFundaT<T>::No &&
                 !CompoundT<T>::IsRefT &&
                 !CompoundT<T>::IsPtrT &&
                 !CompoundT<T>::IsPtrMemT &&
                 sizeof(enum_check(ConsumeUDC<T>()))==1 };
    enum { No = !Yes };
};