On Mar 15, 2010, at 4:59 PM, Daniel James wrote:
On 15 March 2010 20:44, Howard Hinnant <howard.hinnant@gmail.com> wrote:
On Mar 15, 2010, at 4:33 PM, Daniel James wrote:
where node_ptr is a nested typedef in the container to unique_ptr<__node, __node_deleter<__node_allocator>>. With this tool one can remove a node from a container, change its value, and insert it back into the container (or another which has an equal allocator). E.g.:
You probably know better than me, but I don't think you can use unique_ptr like that with the new allocator requirements.
Just for clarity's sake, the unique_ptr should hold a reference to the container's deleter, not a copy. So users of the node_ptr would need to watch out for lifetime issues (the node_ptr should not outlive the container which produced it). I consider that a small price to pay for the functionality/performance gained. But it /is/ inventive.
Sorry, I should have been clearer, I was worried about the node pointer. I don't think you can use a '__node*' with the new allocator requirements. You can obviously get a pointer by from a reference, but there doesn't seem to be a way to get 'allocator_type::pointer' back later, since there's no longer a requirement for 'allocator::address'.
Ah! Excellent point. If I'm missing your point just let me know. But the way to handle this is to have your custom deleter make its node_pointer type the same as the node_allocator's node_pointer type. unique_ptr will then use it for the storage. template <class _Alloc> class __hash_node_destructor { typedef _Alloc allocator_type; typedef allocator_traits<allocator_type> __alloc_traits; public: typedef typename __alloc_traits::pointer pointer; // unique_ptr<T, __hash_node_destructor<A>> uses this for its pointer type ... }; The container will want to rebind its user-supplied allocator into a node allocator and then instantiate its node_destructor with that. Now when the node_destructor calls __alloc_traits::deallocate, it is passing the same pointer type that the allocator expects. It helps if you already have allocator_traits implemented for all of this. hth, Howard