Re: [boost] shared_ptr - allocator template argument

From: Michael Goldshteyn (mgoldshteyn_at_[hidden])
Date: 2005-11-14 11:08:53

"Peter Dimov" <pdimov_at_[hidden]> wrote in message 
news:002801c5e56a$a6d88930$6401a8c0_at_pdimov2...
> Michael Schneider wrote:
>
>> Is there a reason why shred_ptr does not accept an allocator?
>
> shared_ptr doesn't have an allocator template parameter because this would
> encode an implementation detail into its type. An important design 
> principle
> of shared_ptr<T> is to hide such specific requirements behind an opaque 
> type
> that just "does the right thing" when it comes to 
> deallocation/destruction.
>
> This doesn't mean that shared_ptr shouldn't accept an allocator, though. 
> The
> proper way to add allocator support would be via an additional 
> constructor:
>
> template<class Y, class D, class A> shared_ptr( Y * p, D d, A a );
>
> and a corresponding reset.
>
> Now in CVS. ;-)
>
>>     - If a change is required, what can I do to help make this change
>>       in boost (I am new to the boost community)?
>
> You can contribute a test for the new functionality. :-)

I don't understand. Looking at sp_counted_impl.hpp, it appears that there 
already is a way to do this in the current shared_ptr implementation, using 
the following steps:

- Define BOOST_SP_USE_QUICK_ALLOCATOR
- Make sure BOOST_SP_USE_STD_ALLOCATOR is not defined
- Create an instance of the quick_allocator class template for the class you 
are using with shared_ptr, redefining the quick_allocator instatiation's 
alloc and dealloc functions as needed

Am I wrong in my interpretation of that code? I will acknowledge, however, 
that your approach above, with the three parameter constructor, is the more 
proper way to add a custom allocator.

Michael Goldshteyn