What are the main purposes of using std::forward and which problems it solves?

Question

In perfect forwarding, std::forward is used to convert the named rvalue references t1 and t2 to unnamed rvalue references. What is the

Answer 1

I think to have a conceptual code implementing std::forward can add to the discussion. This is a slide from Scott Meyers talk An Effective C++11/14 Sampler

Function move in the code is std::move. There is a (working) implementation for it earlier in that talk. I found actual implementation of std::forward in libstdc++, in file move.h, but it is not at all instructive.

From a user's perspective, the meaning of it is that std::forward is a conditional cast to an rvalue. It can be useful if I am writing a function which expects either an lvalue or rvalue in a parameter and wants to pass it to another function as an rvalue only if it was passed in as an rvalue. If I did not wrap the parameter in std::forward, it would be always passed as a normal reference.

#include 
#include 
#include 

void overloaded_function(std::string& param) {
  std::cout << "std::string& version" << std::endl;
}
void overloaded_function(std::string&& param) {
  std::cout << "std::string&& version" << std::endl;
}

template
void pass_through(T&& param) {
  overloaded_function(std::forward(param));
}

int main() {
  std::string pes;
  pass_through(pes);
  pass_through(std::move(pes));
}

Sure enough, it prints

std::string& version
std::string&& version

The code is based on an example from the previously mentioned talk. Slide 10, at about 15:00 from the start.