[boost] Re: calling bind with literals

From: David Abrahams (dave_at_[hidden])
Date: 2004-05-06 20:50:24

Douglas Gregor <gregod_at_[hidden]> writes:

> On Thursday 06 May 2004 05:32 pm, Dill, John wrote:
>> I believe that this can be done, but doesn't justify whether it should be
>> done.  There are several issues that I see at the moment.
>>
>> A.  Changes the semantics of everyone's bind and mem_fn, no biggy there
>> ;-). B.  Pass by value is silent, not sure how many copies of the argument
>> will be generated if pass-by-value.
>>
>> But at the same time there is an advantage.
>>
>> a.  You can use literals in calling your bind functions.
>>
>> What do you all think?
>
> I don't like the change.
>
> Ideally, bind(f, _1, _2, _3)(x, y, z) would be exactly equivalent to f(x, y, 
> z). The current bind() implementation gives us nearly this equivalence 
> because it passes by reference, except that we get a failure at compile time 
> if one tries to pass a literal. 

Or any rvalue for that matter.

> Going to passing by value would take us further from that ideal
> equivalence.

I agree.  IMO the best answer for now is to generate the 2^N overloads
of operator() for some user-selectable N.  Unary and binary functions
are so common that IMO usually N==2 will do it.

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com