问将函数标识符作为右值引用传递，并对其应用std::move()

EN

#include <iostream>
#include <functional>

using callback = std::function<double (double, double)>;


double sum (double a, double b) {
    return a + b;
}


int main (int argc, char *argv[]) {
    // Shouldn't this leave sum() in an invalid state?
    auto c = std::move(sum);

    std::cout << c(4, 5) << std::endl;
    std::cout << sum(4, 5) << std::endl;

    return EXIT_SUCCESS;
}