"David Abrahams" <dave@boost-consulting.com> escribió en el mensaje news:u3bvwtvvq.fsf@boost-consulting.com...
"Peter Dimov" <pdimov@mmltd.net> writes:
David Abrahams wrote:
"Joe Gottman" <jgottman@carolina.rr.com> writes:
I disagree. This may ensure the basic exception-safety guarantee, but most code that uses optional<T> will use T::operator=() at some point or other. So if T::operator=() is not exception-safe
Whoa, here we go again! You seem to be assuming
basic exception-safety guarantee == "not exception-safe."
That's just not true for any reasonable definition of "exception-safe."
No, he isn't assuming that. "Not exception safe" == "does not provide basic" in the above paragraph. Fernando's goal, IIUC, was to make optional<T>::operator= provide the basic guarantee even when T::operator= does not. We are arguing that this is not necessary
Agreed. There's no good reason to try to "fix" broken classes.
and that optional<T>::operator= should just mirror the exception safety guarantee of T::operator= and T::T( T const & ).
Sounds fine to me.
Well, I'm kind of sure that this was discussed before when Boost.Optional was being reviewed and the conclusions were the opposite... but maybe I just got it wrong. I have to admit that on a fresh look at it I can only agree with Peter here regarding the unwarranted additional guarantees from Optional. That being said, I'm still unsure that the overhead of the swap idiom is worth it in this case were the swap isn't no-throw (that is, given that the idiom does not provide by itself any additional guarantees) The correct fix along Joe's initial proposal would be: void assign(optional_base const& rhs) { if (is_initialized) { if ( rhs.is_initialized ) get_impl() = rhs.get_impl(); else destroy(); } else { if ( rhs.is_initialized ) construct(rhs.get_impl()); } } AFAICS, this code is as safe aliasing-wise as it can be (it handles not only the trivial case of this==&rhs but also any other deeper aliasing issues) If no voice is raised I'll proceed with this fix. Best, Fernando Cacciola