Method operator()

test/function_traits_test.cpp:63–66

struct CcI2SStrctNoexcept {
    std::string operator()(const std::string& str, int x) noexcept
    {
        return CcI2SFreeNoexcept(str, x);
    }
    std::string nonCMemF(const std::string& str, int x) noexcept
    {
        return CcI2SFreeNoexcept(str, x);