Re: [boost] [function] allocator template parameter question

From: Douglas Gregor (doug.gregor_at_[hidden])
Date: 2007-06-07 22:47:55

On Jun 7, 2007, at 10:21 PM, Emil Dotchevski wrote:
> I am storing the allocator, in struct functor_wrapper from
> function_base.hpp, but it has a partial specialization for  
> std::allocator
> which doesn't store the allocator, and perhaps that's what you saw.  
> Please
> take another look:
>
> http://www.revergestudios.com/boost-function/function_base.hpp
>
> Of course if the function object can use the small object  
> optimization, the
> functor_wrapper template is not used and no copy of the allocator  
> is stored
> in the boost::function.

Ah, right. I was looking at part of the code where the allocator  
wasn't being passed on, but of course that part of the code didn't  
need to do any allocation. Two comments:

   (1) Often, one inherits from the allocator rather than storing it  
in a member. That way, if the allocator type is empty, we don't need  
to use up any storage.
   (2) Visual C++ strikes again: we'll have to #ifdef out these  
allocator versions for Microsoft's compiler prior to version 7.1,  
both because of the reliance on partial specialization of class  
templates and because of the use of rebind.

>> I haven't done a thorough review of the code, but I'd be inclined to
>> move boost::function toward this approach. It's a better extension to
>> tr1::function than the existing code, and it might be the right way
>> for C++0x's "function" to go. If you're interested in this feature
>> going into the next standard, I suggest writing a short proposal to
>> the C++ Library Working Group for this extension.
>
> Will do.

Looking forward to it. If you write it soon, it should get on the  
agenda for the July meeting of the C++ committee. I expect it will be  
easily accepted.

        - Doug