Jeffrey Hellrung escribió:
Hi (again) Ion,
I recently ran into the following issue. I defined a copyable-and-movable class X, and class Y has a member variable of type X and no other member variables. It thus (apparently) happens that Y's auto-generated operator= takes a non-const reference to Y, which I would guess is generally not desired, or at least an operator= overload taking a const reference to Y should be available.
Yes, I recently got the same issue in Interprocess. The standard says that the auto-generated assignment takes non-const argument if any of bases or members' assignment is non-const. Since we generated the non-const version with Boost.Move, assignment operators are not generated with const arguments. In this case the only solution is to avoid compiler-generated assignment operator and write an explicit one. Copy constructor does not suffer this because we rely on RVO to avoid copies. The fact that you need to add *both* const and non-const is strange, in my case, just definining the const version in the higher-level class was enough.
The only point I want to make is that it seems worth mentioning this subtlety (at least it was a subtlety to me) in the move documentation somewhere, and perhaps how to most easily and portably address this (I'm not sure what that would be), as I would expect it to be a not uncommon situation.
Yes, I should warn about this issue.
- Jeff
Ion