Re: [boost] boost::result_of and C++03

From: Felipe Magno de Almeida (felipe.m.almeida_at_[hidden])
Date: 2008-04-10 01:05:38

On Wed, Apr 9, 2008 at 11:11 PM, shunsuke <pstade.mb_at_[hidden]> wrote:
> Eric Niebler wrote:
>  > Anyway, about the rvalue_wrapper<> Shunsuke proposed and I just
>  > endorsed. The issue is that today, users are writing code like this:
>  >
>  >    int const i = 0;
>  >    fusion::tuple<int> t = fusion::make_tuple(i);
>  >
>  > This is arguably wrong because it is storing an lvalue by value. This is
>  > probably more correct:
>  >
>  >    int const i = 0;
>  >    fusion::tuple<int const &> t = fusion::make_tuple(i);
>
>  It seems to depend on context or domain.
>  Proto may expect it, but
>
>      int const i = 0;
>      return fusion::make_tuple(i);
>
>  would be "ouch".

Also would be "ouch" for:

struct handler
{
  typedef void result_type;
  result_type operator()(int i) const
  {
  }
};

int const i = 0;
sock_->async_read( buffer, fusion::fused(handler(), fusion::make_vector(i)) );

>  BTW, Egg offers "pack", which captures all the arguments by-reference.

I prefer by-value by default. Afterall, C++ is a value-based language.

[snip]

>  As shown above, lvalue/rvalue-ness doesn't guarantee the complete safety.
>  FWIW, I usually prefer compatibility. :-)

I would say lvalue/rvalue-ness are safe only when used for reusing temporaries.

>  Regards,
>  --
>  Shunsuke Sogame

Regards,
-- 
Felipe Magno de Almeida