Re: [boost] portable precise garbage collector for C++

From: Achilleas Margaritis (axilmar_at_[hidden])
Date: 2007-09-22 09:00:15

O/H Sebastian Redl έγραψε:
> Larry Evans wrote:
>> BTW, I'm trying to do std::list<T> correctly; however,
>> I'm having problems.  It appears allocator::pointer
>> doesn't help when using:
>>
>>    struct node
>>    {
>>       T elem;
>>       node* next_;
>>       node* prev_;
>>    };
>>
>> because the begin/end pointers are to node* not to T*.
>>   
> That's what the rebind mechanism is for. Suppose your allocator
> parameter is Alloc:
> 
> template<typename T, typename Alloc = std::allocator<T> >
> class list
> {
> };
> 
> Then first you need the node allocator:
> 
> typedef typename Alloc::template rebind<node<T> >::other node_allocator;
> 
> Then you can get the new allocator's pointer type:
> 
> typedef typename node_allocator::pointer node_ptr;
> 
> class node
> {
>   T elem;
>   node_ptr next;
>   node_ptr prev;
> };
> 
> Don't forget to construct the node_allocator member you'll hold from the
> allocator you're passed in. All allocators must have a templated
> constructor for this purpose.
> Something most implementations do, by the way, is that they are written
> in such a way that EBO applies to the allocator if it has no state.
> 

But STL containers do not use the rebind struct for their internal 
allocations or for their member pointers. They just use T* instead of 
allocator<T>::rebind<U>::pointer.