Re: [Boost-users] [Any] inconsistent return types of any_cast overloads

Subject: Re: [Boost-users] [Any] inconsistent return types of any_cast overloads
From: Krzysztof Czainski (1czajnik_at_[hidden])
Date: 2013-12-04 07:07:32

2013/12/4 Arne Vogel <avogel_at_[hidden]>

>  On 03.12.2013 00:01, Krzysztof Czainski wrote:
> [...] what do you gain by doing:
>
>   const auto& vec = boost::any_cast<std::vector<int>>(makeVec());
>  instead of
>   const auto vec = boost::any_cast<std::vector<int>>(makeVec());
>  ?
>
>  Regards,
> Kris
>
>
> In C++11 with a moveable type, probably not much. I don't quite remember
> why I wrote the code like this - it could have been out of habit since in
> C++98 using a reference may save a copy, though I guess an optimizing
> compiler had already been allowed to elide it.
>

I'm just curious to know if anyone uses a compiler that doesn't actually
elide the copy (or move) in this case ;-) In all discussions about this
I've never seen someone actually name one, but still they try to avoid the
copy just in case.

I think taking values returned by value by const & to extend their lifetime
should be deprecated in new C++ - compilers could then warn not to do it.

Cheers,
Kris