I tried to implement it as the following, with all of auto, decltype() and std::forward<>().

Is there any simpler implementation?

#include <vector>
using namespace std;

template<typename T>
auto foo(T &&t) -> decltype(t) {
    return std::forward<T>(t);
}

int main() {
    vector<int> v{0, 1};
    vector<int> v0 = foo(v); // OK, copy ctor
    vector<int> &v1 = foo(v); // OK, reference

    vector<int> v2 = foo(vector<int>{0, 1}); // OK, ctor with rvalue
    // vector<int> &v3 = foo(vector<int>{0, 1}); // Error, as expected

    return 0;
}