"Scott McMurray" <me22.ca+boost@gmail.com> wrote in message news:fa28b9250808290914l19a6cf1fue658229148ec0f09@mail.gmail.com... [...]
It's not an allocator, and it's often useful in strange ways:
shared_ptr<FILE> f( fopen("file.txt"), fclose );
The fact that the deleter is specified on initialization is also essential in that it allows you to create shared_ptrs to incomplete types:
struct S { auto_ptr<S> p; }; // illegal struct S { shared_ptr<S> p; }; // fine
So I don't really see your point, here.
I think you're confusing the allocator and the deleter but I am exclusively referring to the allocator. I just looked at the code of shared_ptr today and it is very similar to what I wrote yesterday: template<class P, class D, class A> class sp_counted_impl_pda: public sp_counted_base { ... virtual void destroy() // nothrow { typedef typename A::template rebind< this_type >::other A2; A2 a2( a_ ); this->~this_type(); a2.deallocate( this, 1 ); // ugh! } }; This is ill-formed code. It's obvious shared_ptr is still in its theoretical stage as far as the allocator is concerned; because std::allocator is a bad example to start with. Let's take a real one like the following: // allocator template <typename T> class my_allocator { boost::fast_pool_allocator pool_; ... void deallocate(pointer & p) { pool_.deallocate(p.release()); // do not touch "this" anymore starting here!! } }; The way shared_ptr works right now, the pool is going to be copied entirely on to the sp_counted_impl_pda object. The problem here is that the pool is going to delete its own instance when deallocate() is called. The allocator variable sp_counted_impl_pda::a_ will need to be changed for a functor or a global function pointer before anything else. Moreover using and allocator explicitly using release() saves some unnecessary overhead for tested classes and library programmers. One might wonder why using a smart pointer for well tested classes? Well it turns out shifted_ptr is much more efficient this way because all node allocations will be part of the same set. -Phil