"Thorsten Ottosen" <tottosen@dezide.com> wrote in message news:<dpk19e$u4$1@sea.gmane.org>...

Thorsten Ottosen wrote:

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Sam Partington wrote:

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It seems to me that the first has the disadvantage of making it relatively easy to provide an incorrect cloner that allows slicing. However this is relatively easy to avoid by making your hierarchy noncopyable, (Perhaps a way around this is to remove the default implementation of new_clone?)

It's not very sensible to make the hierarchy copyable, because you can run into slicing in other places then.

As for the default, then I've been thinking about this too. It still won't catch that one missed a clone() function longer down the hiararchy.

Hm...I just came to think that a little assertion might help us out here:

inline base* new_clone( const base& b ) { base* res = b.clone(); assert( typeid(*res) == typeid(b) ); return res; }

That should catch any problems. I can even put this inside the clone-allocator, so the user don't have to specify this.

That's a good idea, and it's something I could also add to cow_ptr and copy_ptr. However, doesn't boost have something better then typeid?