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Subject: Re: [boost] [variant2] documentation request
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2019-03-04 18:00:08

On Mon, Mar 4, 2019 at 7:46 AM Niall Douglas via Boost <
boost_at_[hidden]> wrote:
> >> > I agree that one can make a good argument for (a variation of) >
> >> double_buffer_variant, which prioritizes strong guarantee over sizeof.
> >> > But that's only needed when your contained types don't have noexcept
> >> > move. In this case, a not unreasonable course of action is to hold
> >> them > by unique_ptr in the variant instead.
> >>
> >> Except I don't want to pay for the dynamic memory allocation.
> >
> > Types that don't have noexcept move typically already allocate. Yes,
> > it's an extra allocation, but going from 1 to 2 is not the same as going
> > from 0 to 1.
> You're thinking of modern code, or code you are permitted to change.
> I'm thinking of code that I am not permitted to change, whose moves are
> not noexcept because somebody forgot to mark them, and it's now written
> into stone for the next five years.

I've heard that some standard libraries used to define such move
constructors. This, by the way, is proof positive that noexcept is
defective: the thing that specifies that something can't throw is,
practically speaking, useless in checking if something may throw.

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