[C++-sig] Re: register_ptr_to_python docs and test
nicodemus at globalite.com.br
Wed Jun 25 04:00:19 CEST 2003
David Abrahams wrote:
>Nicodemus <nicodemus at globalite.com.br> writes:
> ^ ^
> < >
>You have this problem throughout. Did you validate your html?
No, I didn't, sorry. But I tested it in mozilla and internet explorer,
and both display it fine. But even checking the text for this kind of
error, I couldn't find any, even this one you're pointing. I guess the
html got mixed up in the sending? It happened before in another doc
>> defines a function that allows the user to register smart pointers for
>> classes with virtual member functions that will be overwritten in
>You mean "overridden" and not "overwritten".
> But this has nothing at all to do with virtual member functions AFAICT.
Yeah, it is because of how the C++ object is held in Python, because of
the wrapper class; but you are right, this paragraph does not explain it
> supplies <code>register_ptr_to_python</code>, a function template
> which registers a conversion from a smart pointers to Python. The
> resulting Python object holds a copy of the converted smart pointer,
> but behaves as though it were a wrapped copy of the pointee. If
> the pointee type has virtual functions and the class representing
> its dynamic (most-derived) type has been wrapped, the Python object
> will be an instance of the wrapper for the most-derived type.
>> Classes that have virtual methods (and the user has supplied a
>> wrapper, <code>X_Wrapper</code>, allowing Python to callback into
>> C++) live in Python not as <code>X</code> objects, but as
>> instances of the wrapper class. This is a problem because
>> conversions to-python of <code>smart_ptr<X></code> objects won't
>> work since the objects that live in Python are held actually by
>> <code>smart_ptr<X_Wrapper></code> instances.
>OK, this is one reason you might want to do use
>register_ptr_to_python, but it's not the only reason.
Sorry, that was the only reason I knew... what's the other?
>> Using the function in this header to register the smart pointer allows
>> correct conversion to-python of <code>smart_ptr<X></code> instances,
>> but has one drawback: a <code>X</code> object created in Python will not be
>> able to be passed as a <code>smart_ptr<X>&</code> argument.
>> But it is still possible to pass a X object created in Python as
>> <code>smart_ptr<X></code>, <code>smart_ptr<X_Wrapper></code>,
>> <code>smart_ptr<X> const&</code>, or
>> <code>smart_ptr<X_Wrapper> const&</code> as an argument.
>That's because, unless X is wrapped with smart_ptr<X> as a template
>argument to its class_<...>, X objects created in Python are held
>directly in the containing Python object.
Using register_ptr_to_python to register the smart pointer
allows correct to-python conversions of smart_ptr
instances, but has one drawback: a X object created in Python
will not be able to be passed as a smart_ptr<X> &
argument because, unless X is wrapped with smart_ptr<X> as
a template argument to its class_<...>, X objects created in Python are
held directly in the containing Python object. But it is still possible to
pass a X object created in Python as smart_ptr<X>,
smart_ptr<X_Wrapper>, smart_ptr<X> const&, or smart_ptr<X_Wrapper> const&
as an argument to a function.
>>Here is an example of a module that contains a class <code>A</code> with
>>virtual methods and some functions that work with
Dave, we can discuss changes here and then I can commit myself, if you want.
More information about the Cplusplus-sig