Re: [boost] [optional] Why was optional<T>::reset() deprecated?

2016-03-02 12:30 GMT+01:00 Andrzej Krzemienski :

2016-03-02 12:21 GMT+01:00 Beman Dawes :

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On Wed, Mar 2, 2016 at 3:20 AM, Andrey Semashev < andrey.semashev@gmail.com> wrote:

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On 2016-03-02 01:51, Andrzej Krzemienski wrote:

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At some earlier stages of development, boost::optional did not have the assignment from boost::none_t (and probably also from T); and reset was the only way to efficiently change the optional from the state of having the value to the state of not having the value.

After the addition of more fancy syntax (conversion to bool, assignment from none_t), reset() (and is_initialized()) became redundant, and hence the deprecation.

I got that from reading Boost mailing archives once.

FWIW, I don't think that having support for 'none' is enough reason to deprecate 'reset' (same for 'is_initialized'). I know some of my

colleagues > who prefer these methods to the fancy syntax because it feels more aligned > with other Boost and standard library components. Having 'reset' also > allows not to include boost/none.hpp. >

The standards committee's library enhancements working group (LEWG) agrees with you. Nevin's question came up in the context of aligning several Library Fundamentals TS functions with each other and the rest of the standard library. The proposal is progressing and will likely be part of C++17.

P0032 http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0032r1.pdf mentions reset() with no arguments. I can un-deprecate this overload when the proposal is accepted. I am not sure about the overload with T: we have a more generalized emplace() for this purpose.

Regards, &rzej

Regarding the broader problem of compatibility between boost::optional and std::optional, I see a bigger issue. Name in_place is already reserved in namespace boost for In-place Factories http://www.boost.org/doc/libs/1_60_0/libs/optional/doc/html/boost_optional/i.... I am not sure how to approach it. Regards, &rzej