I have some code that has been merrily using the 1.32.0 release of boost, including boost::optional, and I've just tried to change to use the 1.33.0 release (this is the first change to this codebase since 1.33.0 was released).
In my code, I have boost::optional<X> where X is copy-constructible, but not assignable. This works in 1.32.0, but fails in 1.33.0. Ouch!
Oh boy.
What is the reason for the change?
I need to dig up the archives to recall the exact reason... I do remeber though that there was a good one. As for the _justification_ for a breaking change, the idea was that if X is non-assignable, then optional<X> should not be assignable either, or at the very least, you don't need it to be assignable. That is, you can always write: optional<X> o ; o = none ; o = v; instead of just o = v ; if X is non-assignable. Anyway, don't you agree that optional<X>::operator= should go through X::operator=? And in that case, is there a choice but to have optional assignment fail with non-assignable types?
Why is this not listed in the "Updated libraries" section of the docs?
Becuase I failed to list it there.
Why is this not listed under the "Type Requirements" section of the docs?
Because I forgot to add it. The specific docs for operator= do mention that T's operator = is used; but you're right I forgot to update the requirements. Anyway, does the "reset it first" trick work for you? Do you think this change has to be rolled back (just asking)? Best, -- Fernando Cacciola SciSoft http://fcacciola.50webs.com/