Class B

test/test_traits.cpp:65–75

    int value = 0;
};
struct B {
    int value = 0;
    B& operator=(B const& b) {
        value = b.value;
        return *this;
    }
    B& operator=(B&& b) {
        value = b.value;
        return *this;
    }
};
struct C {
    int value;
    template <class U>