on Mon Feb 11 2013, "Peter Dimov" <lists-AT-pdimov.com> wrote:
Jeffrey Lee Hellrung, Jr. wrote: On Mon, Feb 11, 2013 at 12:01 PM, Ralph Tandetzky < ralph.tandetzky@googlemail.com> wrote:
Nice idea though. write_ptr<T> would behave like value_ptr<T>
Not as I understand it; write_ptr would behave similar to unique_ptr, i.e., it would be move-only.
You could, in principle, make it do a deep copy, but the point of the exercise is to avoid inadvertent expensive copies, so a move-only pointer makes a bit more sense, I think. An explicit copy() could perform the deep copy, if needed.
Nit: there is no such thing as "deep copy." :-)
On the other hand, making it do a deep copy is slightly more flexible because you could then use it as a value_ptr if you don't care for the whole CoW business. I could go either way on that.
Random thoughts: I don't know where this discussion stands on the issue, but it just occurred to me that I wouldn't want copying a ptr to automatically do anything to the ptee (pointee). I could imagine something like shared_ptr taking an optional cloner (as well as a deleter) and having shared_ptr<T const> x(new T); shared_ptr<T> y = x.clone_ptee(); I like the way const qualification integrates with that. I wonder if everyone who wants to implement CoW also wants the cost of shared_xxx, though. -- Dave Abrahams