20.06.2011, в 21:55, David Levin написал(а): > PassRefPtr is useful even if the function doesn't take any kind of ownership. > It's useful when callers want to get rid of ownership, and then they can do > that efficiently. > > I don't understand this. How it is more efficient to pass ownership if a > function isn't taking ownership? It seems like passing in a raw pointer would > be the most efficient in this case.
As a concrete example, consider a callback function. It can take a reference to an object as an argument - the caller definitely no longer needs this object after calling it, while the function may or may not take ownership (in any sense of this word). In an extreme case, it will not look at its argument at all. Similarly, a base class implementation of a virtual member function may not do anything with its argument, while derived objects will "take ownership". It's not easy to tell if any of the overrides do (or will in the future) take ownership. Yet it's easy to see if ownership is being passed away at call sites. - WBR, Alexey Proskuryakov
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