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

How would that affect the called function inner if we leave t1 & t2 as lvalue?

If, after instantiating, T1 is of type char, and T2 is of a class, you want to pass t1 per copy and t2 per const reference. Well, unless inner() takes them per non-const reference, that is, in which case you want to do so, too.

Try to write a set of outer() functions which implement this without rvalue references, deducing the right way to pass the arguments from inner()'s type. I think you'll need something 2^2 of them, pretty hefty template-meta stuff to deduce the arguments, and a lot of time to get this right for all cases.

And then someone comes along with an inner() that takes arguments per pointer. I think that now makes 3^2. (Or 4^2. Hell, I can't be bothered to try to think whether const pointer would make a difference.)

And then imagine you want to do this for a five parameters. Or seven.

Now you know why some bright minds came up with "perfect forwarding": It makes the compiler do all this for you.