Re: [boost] Boost.Convert. Take 2.

Subject: Re: [boost] Boost.Convert. Take 2.
From: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2014-02-21 04:38:44

2014-02-21 10:31 GMT+01:00 Vladimir Batov <vb.mail.247_at_[hidden]>:

> > Andrzej Krzemienski <akrzemi1 <at> gmail.com> writes:
> > ...
> > If you added MoveConstructible requirement (I am not saying you should, I
> > am just exploring the possibility), you would be probably saying "It also
> > works with non-CopyConstructible but MoveConstructible types, but in that
> > case there is a limited number of ways Boost.Convert's interface can be
> > used." The above example would not work, but the following one should:
> >
> > convert<std::string>::from(12345, cnv).value_or("bummer");
> >
> > That is, you do not care that a temporary's internal value is moved from.
> > But this may not be implementable in C++03. I guess we do not know how to
> > emulate rvalue references for *this. However, the following should be
> easy
> > to implement:
> >
> > convert<std::string>::from(12345, cnv).value();
> >
> > For some background, move semantics obtained a nice language support in
> > C++11, but it is also available in C++03 for some extent. This is why we
> > have Boost.Move. I will try to add move semantics to Boost.Optional, so
> > that you can use it.
>
> RE: convert<>::from().value();
>
> This one is fine as it returns a const reference (unless it throws. So, no
> additional requirements whatsoever... right?
>

Well, now that I think of it: implementing it may also require "rvalue
references from *this" feature, which may not be implementable in C++03.

>
> RE: MoveConstructible
>
> I do think that your clarifications should be in the docs and Rob's
> std::move() deployment in the code. Still, I feel that this sort of
> detailed
> explanations/clarifications/implementation could wait... until we decide if
> we want to proceed any further with "convert"... I just do not want our
> effort wasted. I hope you understand my hesitation.

Agreed.