Perfect Forwarding the "Hello World!"

I’ve been going back and forth understanding lvalue and rvalue. Here is an attempt of mine in explaining it

So here is a cool “Perfect Forwarding” Hello, World! code implementation using C++. When std::string{"World!"} is passed, this is a prvalue (a “temporary”) aka an rvalue expression. T is deduced to std::string, becoming say_hello(std::string && name_param). In the other case, when instead the variable name is passed, this is a variable aka an lvalue, T is deduced to std::string& becoming say_hello(std::string& && name_param), the && will get reduced (reference collapsing rules), therefore finally becoming say_hello(std::string& name_param).

std::forward<T> restores the value category (lvalue/rvalue) of the original argument expression by conditionally casting the named parameter to the value category encoded in T, hence “Perfect Forwarding” (same type, same cv-qualification, same value category).

#include <print> 
#include <string>
#include <utility>

template <typename T>
void say_hello(T&& name_param) {
   std::println("Hello, {}", std::forward<T>(name_param)); 
}

int main() { 
    say_hello(std::string{"World!"}); 
    
    std::string name = "Matt!";
    say_hello(name); 
  
    return 0; 
}