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

From: Peter Dimov (pdimov_at_[hidden])
Date: 2007-11-01 13:51:32

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?