check function exist

function_check.cpp

#include <iostream>

int f(int x) {
    std::cout << "true f" << std::endl;
    return 0;
}

namespace bbb {
    struct function_is_not_exist {};
    function_is_not_exist f(...) { return {}; };
    using check_f = std::is_same<decltype(f(0)), function_is_not_exist>;
}

template <typename type, typename = std::enable_if<std::is_same<type, int>::value>>
auto f(type x) -> typename std::enable_if<bbb::check_f::value, int>::type {
    std::cout << "dummy f" << std::endl;
    return 0;
}

int main(int argc, char *argv[]) {
    f(0);
    return 0;
}