On 5/29/2015 7:28 AM, Stefan Seefeld wrote:
Python's copy module allows for objects to be copied. The protocol for this will look up special method __copy__. It seems to me that this would trivially work for C++ objects providing a copy-constructor. However, the copy-constructor isn't automatically bound to __copy__. While I can certainly add that in user-code, I wonder why this isn't done by Boost.Python itself. Does anyone know the reasons for this ? Would it seem useful to add that feature ?
The __copy__ method's intended semantics are to produce a "shallow" copy while the __deepcopy__ method is meant to produce a "deep" copy. Given a C++ class with a copy ctor, it's hard to know which is more appropriate. For instance, copying a shared_ptr<T> is like a "shallow" copy but copying a vector<pair<int, float>> is like a deep copy. On the other hand copying a vector<shared_ptr<T>> is more like a shallow copy.
I wouldn't mind an opt-in convenience utility that adds a __copy__ or __deepcopy__ method, but given the semantic subtlety, I think trying to do it automatically is dicey.
Also, adding a feature to do it automatically could potentially interfere with existing binding code that manually provides __copy__/__deepcopy__ methods.
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