Re: [boost] [variant] Heads-up!

Subject: Re: [boost] [variant] Heads-up!
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2019-04-29 20:00:29

On Mon, Apr 29, 2019 at 12:47 PM Steven Watanabe via Boost <
boost_at_[hidden]> wrote:
>
> AMDG
>
> On 4/29/19 1:08 PM, Antony Polukhin wrote:
> > <snip>
> > This discussion was considered. Please see the two comments from
> > Nikita Kniazev
https://github.com/boostorg/variant/pull/59#issuecomment-459573177
> >
>
> From the PR:
> > The nullified recursive_wrapper is in a valid but unspecified state
>
> Strictly speaking this is true, but it is
> backwards incompatible because the state
> was not valid in previous versions.

This makes it sound like the only problem is that it is a breaking change,
but just because we label that state as "valid" doesn't mean that we can
also say that we're providing the never-empty guarantee. If we care about
correctness at all, if the never-empty guarantee is not dropped, the state
in question is not valid and therefore we're violating the basic guarantee.