测试reference_wrapper

#include <iostream>
#include <functional>
void add(int a, int b, int &r) {
    r = a + b;
}
int main() {
    int r = 0;
    auto f = std::bind(add, std::placeholders::_1, 20, std::reference_wrapper<decltype(r)>(r));
    f(10);
    std::cout << r << std::endl;

    return 0;
}