Re: [boost] [variant] Please vote for behavior

Subject: Re: [boost] [variant] Please vote for behavior
From: Dave Abrahams (dave_at_[hidden])
Date: 2013-01-30 20:33:29

on Tue Jan 29 2013, Paul Smith <pl.smith.mail-AT-gmail.com> wrote:

> On Tue, Jan 29, 2013 at 7:25 PM, Jeffrey Lee Hellrung, Jr.
> <jeffrey.hellrung_at_[hidden]> wrote:

>> This discussion might be facilitated if Joel et al (sorry Joel, I don't
>> mean to pick on you, I just mean the group arguing for introducing this
>> "singular" post-move state) simply said "yes, we understand we're making a
>> breaking change (by possibly introducing an additional state to variant
>> that violates the never-empty guarantee), but we still think it's the most
>> practical approach to introduce efficient move semantics to variant". I can
>> jive with that but I think Paul's concerned that you (again, as a
>> representative of the platform you're taking) don't appreciate that this is
>> a breaking change to variant.
>
> I think this is about a little more than that, even though to be
> honest, I'm not entirely sure what's the dispute is about too.
> I think it's closer to what Edward Diener said:
>
>   The main issue seems to be simply this: are guarantees ( invariants )
>   for an object of a class meant to cover moved from objects of that
>   class?

I don't think that question should really even be on the table.  If
"invariant" and "guarantee" are to have any useful meaning, the answer
must be "yes."

-- 
Dave Abrahams
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