Understanding rvalue references

Question

I think there\'s something I\'m not quite understanding about rvalue references. Why does the following fail to compile (VS2012) with the error \'foo\' : cannot conver

Answer 1

I always remember lvalue as a value that has a name or can be addressed. Since x has a name, it is passed as an lvalue. The purpose of reference to rvalue is to allow the function to completely clobber value in any way it sees fit. If we pass x by reference as in your example, then we have no way of knowing if is safe to do this:

void foo(int &&) {}
void bar(int &&x) { 
    foo(x); 
    x.DoSomething();   // what could x be?
};

Doing foo(std::move(x)); is explicitly telling the compiler that you are done with x and no longer need it. Without that move, bad things could happen to existing code. The std::move is a safeguard.

std::forward is used for perfect forwarding in templates.