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

From: Douglas Gregor (doug.gregor_at_[hidden])
Date: 2007-06-04 23:24:55

On Jun 4, 2007, at 10:57 PM, Emil Dotchevski wrote:
> One important advantage of using boost::function is that it acts  
> like a
> function pointer, reducing physical coupling between compilation  
> units. This
> is very much like shared_ptr.
>
> A nice feature of shared_ptr is that it has a single template  
> parameter, T,
> even though diferent instances of shared_ptr<T> can use different
> allocators.
>
> When using boost::function, one can also provide an allocator, but  
> unlike
> shared_ptr, the allocator is a default parameter of the  
> boost::function
> class template.

> Is there a reason why this is necessary? Can't boost::function use  
> similar
> technique to the one employed by shared_ptr to avoid the need for this
> second template parameter?

You know, I never even thought about adding it. I didn't know about  
the shared_ptr technique when I put the allocator into  
boost::function, and after the C++ committee removed the allocator I  
didn't think about it any more.

The biggest issue with moving the allocator into the constructor  
(like shared_ptr) is that boost::function doesn't know what type it  
is going to be interacting with... shared_ptr<T> knows it's 'T',  
function does not. However, I think we can work around this issue. It  
certainly would be better to have the allocator supplied in the  
constructor.

I don't know when I would have time to implement this, although I  
would certainly consider adding this functionality to Boost's  
"function". Might you be interested in implementing it?

        - Doug