Re: [Boost-users] Re: Re: Re: result_of tutorial

From: Peter Dimov (pdimov_at_[hidden])
Date: 2005-03-16 11:49:49

Ian McCulloch wrote:
> Peter Dimov wrote:
>
>> Ian McCulloch wrote:
>>>
>>> Yes, if you want to forward to a function but you don't know if it
>>> takes arguments by value or const reference.
>>
>> It doesn't matter. When you forward, you pass to result_of the exact
>> types of the arguments you are supplying in the function (object)
>> call, with a reference when the argument is an lvalue.
>>
>> int x;
>> long y;
>> int const z;
>> int g();
>> int & h();
>>
>> f(x, y); // result_of<F(int&, long&)>
>> f(1, x); // result_of<F(int, int&)>
>> f(z, 4); // result_of<F(int const&, int)>
>> f( g(), h() ); // result_of<F(int, int&)>
>>
>> What is 'f' and how it takes its arguments in the cases above does
>> not affect how result_of is used.
>
> But what happens if F doesn't have an operator() overload that takes
> F(int const&, int) but only has F(int, int) ?  It seems you need to
> know this in advance.

No, you don't have to know this in advance. It is up to the implementation 
or specialization of result_of<F(...)> to handle these cases and return the 
correct result.