type6.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.
 */
template<typename T>
class IsFunctionT {
  private:
    typedef char One;
    typedef struct { char a[2]; } Two;
    template<typename U> static One test(...);
    template<typename U> static Two test(U (*)[1]);
  public:
    enum { Yes = sizeof(IsFunctionT<T>::test<T>(0)) == 1 };
    enum { No = !Yes };
};

template<typename T>
class IsFunctionT<T&> {
  public:
    enum { Yes = 0 };
    enum { No = !Yes };
};

template<>
class IsFunctionT<void> {
  public:
    enum { Yes = 0 };
    enum { No = !Yes };
};

template<>
class IsFunctionT<void const> {
  public:
    enum { Yes = 0 };
    enum { No = !Yes };
};

// same for void volatile and void const volatile
//...

template<typename T>
class CompoundT {           // primary template
  public:
    enum { IsPtrT = 0, IsRefT = 0, IsArrayT = 0,
           IsFuncT = IsFunctionT<T>::Yes,
           IsPtrMemT = 0 };
    typedef T BaseT;
    typedef T BottomT;
    typedef CompoundT<void> ClassT;
};