On 29/11/2007, Warren Young <mysq...@etr-usa.com> wrote:

No! :) Yes it happens implicitly, that's precisely the point. How many times does self-assignment happen? Seriously. It is almost always the result of a programming error, or maybe occasionally setting a collection of objects to a single value which happens to be in the collection _occasionally_ - let's generously assume it's 0.1% of all assignments. If it does happen, and your class isn't safe for self-assignment, very bad things happen. Nasal demons and all sorts. So we've all learnt to prevent that. But checking if (this ==&rhs) on *every* assignment is what's really wasteful. In 99.9% of assignments the rhs.use_count() goes up, and this->use_count() goes down. It's only wasteful in the 0.1% of cases where this == &rhs and the same refcount goes up and down. So by putting the explicit check back you've helped that tiny fraction of cases, at the expense of the common case. Providing an O(1) nothrow swap, and implementing the assignment operator in terms of copy and swap is the canonical assignment operator. And in The Future (cue sci-fi music) will be even more efficient thanks to rvalue-references and move-semantics.

Pleeeeeease remove it :)

Jon