Move Semantics and Pass-by-Rvalue-Reference in Overloaded Arithmetic

Question

I am coding a small numeric analysis library in C++. I have been trying to implement using the latest C++11 features including move semantics. I understand the discussion and to

Answer 1

You should prefer overloading the operators as free functions to obtain full type symmetry (same conversions can be applied on the left and right hand side). That makes it a bit more obvious what you are missing from the question. Restating your operator as free functions you are offering:

T operator+( T const &, T const & );
T operator+( T const &, T&& );

But you are failing to provide a version that handles the left hand side being a temporary:

T operator+( T&&, T const& );

And to avoid ambiguities in the code when both arguments are rvalues you need to provide yet another overload:

T operator+( T&&, T&& );

The common advice would be to implement += as a member method that modifies the current object, and then write operator+ as a forwarder that modifies the appropriate object in the interface.

I have not really thought this much, but there might be an alternative using T (no r/lvalue reference), but I fear that it will not reduce the number of overloads you need to provide to make operator+ efficient in all circumstances.