Is default constructor elision / assignment elision possible in principle?

Question

. or even allowed by the C++11 standard?

And if so, is there any compiler that actually does it?

Here is an example of what I mean:

template&         


        

Answer 1

Elision of default copy/move assignment operators is allowed based on the general as-if rule only. That is the compiler can do it if it can ascertain that it will have no observable effect on behaviour.

In practice the as-if rule is used in general fashion to allow optimizations at intermediate representation and assembly levels. If the compiler can inline the default constructor and assignment, it can optimize them. It won't ever use the code of the copy constructor for it, but for their default implementations it should end up with the same code.

Edit: I answered before there was the code sample. Copy/move constructors are elided based on explicit permission to the compiler to do so, therefore they are elided even if they have observable effect (printing "COPY"). Assignments can only be elided based on as-if rule, but they have observable effect (printing "ASSIGN"), so the compiler is not allowed to touch them.