C++: What is perfect forwarding in C++?

1#include <utility>
2
3// Universal reference
4template<typename T>
5void wrapper(T&& arg) {
6    // Forward preserving value category
7    func(std::forward<T>(arg));
8}
9
10void func(int& x) {
11    std::cout << "lvalue\n";
12}
13
14void func(int&& x) {
15    std::cout << "rvalue\n";
16}
17
18int main() {
19    int x = 10;
20    wrapper(x);        // lvalue — calls func(int&)
21    wrapper(20);       // rvalue — calls func(int&&)
22    wrapper(std::move(x));  // rvalue — calls func(int&&)
23}