返回值类型后置

#include <iostream>
using namespace std;

//template<typename R,typename T,typename U>
//R add01(T t, U u)
//{
//    return t + u;
//}


template <typename T, typename U>
auto add(T t, U u)->decltype(t + u)
{
    return t + u;
}

int main()
{
    int x = 520;
    double y = 13.14;
    auto ret = add<int, double>(x, y);
    auto ret01 = add(x, y);
    cout << ret << endl;
    cout << ret01 << endl;
    return 0;
}