move-functor.cpp

// Also available here:
// https://godbolt.org/z/CAmvFF

#include <functional>
#include <memory>

struct MyFunctor {
    MyFunctor() : x(0) {}
    MyFunctor(MyFunctor const& rhs) : x(1) {}
    MyFunctor(MyFunctor&& rhs) : x(2) {}

    int operator()() const { return x; }

    int x;
};

int F(MyFunctor&& f) {
    auto tmp = [f]() {
        return f();
    };

    return tmp();
}

int G(MyFunctor&& f) {
    auto tmp = [t = std::move(f)]() {
        return t();
    };

    return tmp();
}

int f = F(MyFunctor()); // f==1 implies copy ctor was called.

int g = G(MyFunctor()); // g==2 implies move ctor was called.

#if WITH_MAIN
#include <iostream>
std::function<int()>  R(MyFunctor&& f) {
    auto tmp = [&f]() {
        return f();
    };

    return tmp;
}

int main() {
    auto fun = R(MyFunctor());

    std::cout << "fun()=" << fun() << std::endl;
    std::cout << "f = " << f << std::endl;
    std::cout << "g = " << g << std::endl;
    return 0;
}
#endif