Re: [boost] reference_wrapper() and operator()()

From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2007-11-01 14:08:21

Peter Dimov skrev:
> Thorsten Ottosen:
> 
>> Doug Gregor skrev:
>>> On Oct 30, 2007, at 6:22 PM, Thorsten Ottosen wrote:
>>>> Is there any good reason that boost::reference_wrapper() does not
>>>> provide a forwarding operator()(), so that we may use it to pass
>>>> function objects by reference to algorithms?
>>> The only reason is laziness. I hacked up a partial implementation in
>>> the sandbox, but I never finished it.
>> Are you using the preprocessor to generate the overloads?
>>
>> One could probably manually provide up to four arguments ... I assume
>> this is more than enough, since the main use-case would be when passing
>> a function object to an algorithm, in which case the mojaority of cases
>> would be 1 or 2 arguments.
> 
> reference_wrapper::operator() needs result_of, and result_of would likely 
> introduce a dependency into Boost.Bind on the PP library, the MPL, type 
> traits, and everything underneath. The change may be worth it even at this 
> cost, but it's not a no-brainer. It might be nicer if we could devise a way 
> to deliver this functionality in a cost-free manner though, perhaps only in 
> tr1::reference_wrapper? 

Oh, totally forgot about this. That sucks.

I would be satisfied with a function

   template< class Return, class T >
   boost::function_obj_ref( const T& );

used like

   algo( first, last, boost::function_obj_ref<bool>( my_heavy_object ) );

-Thorsten