What is “rvalue reference for *this”?

Question

Came across a proposal called \"rvalue reference for *this\" in clang\'s C++11 status page.

I\'ve read quite a bit about rvalue references and understood them, but I

Answer 1

There is an additional use case for the lvalue ref-qualifier form. C++98 has language that allows non-const member functions to be called for class instances that are rvalues. This leads to all kinds of weirdness that is against the very concept of rvalueness and deviates from how built-in types work:

struct S {
  S& operator ++(); 
  S* operator &(); 
};
S() = S();      // rvalue as a left-hand-side of assignment!
S& foo = ++S(); // oops, dangling reference
&S();           // taking address of rvalue...

Lvalue ref-qualifiers solve these problems:

struct S {
  S& operator ++() &;
  S* operator &() &;
  const S& operator =(const S&) &;
};

Now the operators work like those of the builtin types, accepting only lvalues.