Understanding eliding rules with regard to c++11

Question

I have been testing with rvalue references and move semantics and want to make sure I understand when a copy should be elided and when it should follow move semantics.

Answer 1

1. Eliding copies and moves is always an optional optimization and the standard offers no guarantees on when it will be done. Elision is different from the compiler choosing move over copy. The language guarantees when move construction or move assignment is chosen according to its normal overload resolution rules.

2. Some compilers offer a flag to turn elision off. gcc and clang have -fno-elide-constructors. MSVC does not have a specific option, but disabling optimization may avoid some elisions (but some can't be turned off no matter what, such as the copy in Foo x = 1;)

3. I don't know of any reason not to elide copies/moves in production builds.

4. Some people had recommended not relying on the 'return value optimizaiton' when returning 'heavy' classes, because RVO isn't guaranteed. Personally I just verified that my compilers were good about it and went ahead with it. Now that objects can be moved you no longer need to worry about whether a compiler supports such optimizations, because even if it doesn't you'll still get moves instead of copies.