#define INDIRECT_ENABLE_IF 1
#define USE_WRAP 1
#define USE_CHAR 1
#define SPECIALIZE_TRUE 1
#define SPECIALIZE_FALSE 1
#define USE_BOOST_ENABLE_IF 1

#define ALLOW_OK 0
#define ALLOW_SFINAE 1

struct false_type {
    static const bool value = false;
};
struct true_type {
    static const bool value = true;
};

#if USE_BOOST_ENABLE_IF

#include <boost/utility/enable_if.hpp>
using boost::enable_if;

#elif INDIRECT_ENABLE_IF

template<bool, class T = void>
struct enable_if_c {
#if !SPECIALIZE_FALSE
    typedef T type;
#endif
};

#if SPECIALIZE_FALSE

template<class T>
struct enable_if_c<false, T> {
};

#endif

#if SPECIALIZE_TRUE

template<class T>
struct enable_if_c<true, T> {
    typedef T type;
};

#endif

template<class Cond, class T = void>
struct enable_if : enable_if_c<(Cond::value), T> {};

#else

template <typename Cond, class T = void>
struct enable_if {
#if !SPECIALIZE_FALSE
    typedef T type;
#endif
};

#if SPECIALIZE_FALSE

template <class T>
struct enable_if<false_type, T> {};

#endif

#if SPECIALIZE_TRUE

template <class T>
struct enable_if<true_type, T> {
    typedef T type;
};

#endif

#endif

template<class T>
struct is_int {
    typedef false_type type;
};

template<>
struct is_int<int> {
    typedef true_type type;
};

template<class T>
struct is_not_int {
    typedef true_type type;
};

template<>
struct is_not_int<int> {
    typedef false_type type;
};

template<class T, class T2>
struct wrap {
    typedef T2 type;
};

template<class T>
struct s {
    typename T::value x;
};

template<>
struct s<int> {
    s(int) {}
    operator int() { return 0; }
};

#if ALLOW_OK ^ USE_CHAR

template<class T>
#if USE_WRAP
typename wrap<
#endif
    typename enable_if<
        typename is_int<T>::type
#if USE_WRAP
    >::type
#endif
    , s<T>
>::type f(T t) {
    return t;
}

#endif

#if ALLOW_SFINAE ^ USE_CHAR

template<class T>
#if USE_WRAP
typename wrap<
#endif
    typename enable_if<
        typename is_not_int<T>::type
#if USE_WRAP
    >::type
#endif
    , s<T>
>::type f(T t) {
    return t;
}

#endif

#include <iostream>

int main() {
#if USE_CHAR
    char x = 'a';
#else
    int x = 1;
#endif
    std::cout << typeid(f(x)).name() << std::endl;
    int i = f(x);
}