определения наличия функции-члена - (C++) 10:31 am

Взято как водится с RSDN, вот ссылка

#include <list>

namespace omni{

template <class T, T val>
struct member_wrapper{};

template <class T>
char test_for_swap(const T&, member_wrapper<void (T::*)(T&), &T::swap>* p = 0);

template <class T>
double test_for_swap(const T&, …);

template <class T>
struct has_member_swap
    static T t;
    static const bool value = (1 == sizeof(test_for_swap(t)));


template<bool b>
struct swapper
    template <class T>
    static void swap(T& t1, T& t2)
    { std::swap(t1, t2); }

struct swapper<true>
    template <class T>
    static void swap(T& t1, T& t2)
    { t1.swap(t2); }

template <class T>
void swap(T& t1, T& t2)
    swapper<has_member_swap<T>::value>::swap(t1, t2);

} // namespace omni

struct noswap{};

int main()
    std::list<intl1, l2;
    omni::swap(l1, l2);
    noswap s1, s2;
    omni::swap(s1, s2);
    int i1, i2;
    omni::swap(i1, i2);
    return 0;

Используется фича компиляторов “Substitution Failure Is Not An Error” (SFINAE). При разборе идеи следует обратить внимание на разницу в типах возвращаемых значений версий шаблона test_for_swap. Он тут самый главный.

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