Robert Dailey skrev:
On Thu, Jun 25, 2009 at 9:41 AM, Thorsten Ottosen < thorsten.ottosen@dezide.com> wrote:
Do you think a stateful custom clone_allocator would allow you to do what you want?
Could you elaborate a bit on what you mean? What state would you give to clone_allocator?
That is up to you. The important fact is that allocator is stored as an object, and/or that you can access and modify that object to your wishes.
Keep in mind that clone_allocator needs to, at some point, be implemented IN the DLL itself, otherwise the correct 'delete' will not be called. Some sort of polymorphism would solve this, that's the most obvious solution I can think of. Either that, or instead of a functor, take a boost::function, and that way I can pass you a function pointer to call for clone allocation/deallocation. There's several easy ways of solving this particular issue that I can see.
But I would be interested in hearing more about the idea you have. I'm not sure I fully understand just yet.
Let me give you an example of what I was trying to do. To avoid storing duplicates of NullObjects, I want to let my clone_allocator 1. don't delete a null object 2. clone a null object by returning just a pointer (i.e. don't allocate anything) This is how I could do that: template<class NullObject> class null_object_clone_allocator { public: typedef NullObject null_object_type; private: const NullObject* null_object_; public: explicit null_object_clone_allocator( const NullObject& x ) : null_object(&r) { } template< class U > U* allocate_clone( const U& r ) const { if( &r == null_object_ ) return null_object_; return new_clone( r ); } template< class U > void deallocate_clone( const U* r ) const { if( r != null_object_ ) delete_clone( r ); } }; boost::ptr_vector<base,null_object_clone_allocator<null_base>> vec( my_alloc) ; -Thorsten