On 17/08/15 02:12 PM, Nikolay Mladenov wrote:
> If you export an abstract class, create an object from python and call
> its virtual from C++ it should not work without the default
> implementation.
The tutorial explains that well:
for the case of an abstract base, use
def("func", bpl::pure_virtual(&Base::func))
which will provide an implementation that does nothing but raise a
Python exception to tell the caller that the method isn't implemented.
For the case with default implementation, the tutorial gives this wrapper:
struct BaseWrap : Base, bpl::wrapper<Base>
{
virtual std::string func() const
{
if (bpl::override f = this->get_override("func"))
return f();
else
return Base::func();
}
std::string default_func() const { return this->Base::func();}
};
and it seems to me much more natural to implement the "default" case
directly in the "else" branch above, rather than add it to the "def()" call.
Stefan
>
> On Mon, Aug 17, 2015 at 8:03 AM, Stefan Seefeld <ste...@seefeld.name
> <mailto:ste...@seefeld.name>> wrote:
>
> Hi,
>
> I'm reviewing the Boost.Python tutorial, and I'm stumbling over the
> section on "Virtual Functions with Default implementations"
>
> (http://boostorg.github.io/python/doc/html/tutorial/tutorial/exposing.html#tutorial.exposing.virtual_functions_with_default_i).
> It mentions the need to provide a separate default implementation
> function as third argument to "def()", without explaining why that is
> needed.
> In fact, I'm trying various alternatives (abstract, non-abstract),
> and I
> can't find a need for it. All my tests work fine without it.
>
> Does anyone know why this is needed, and could perhaps even provide a
> little test case ?
>
> Thanks,
> Stefan
>
> --
>
> ...ich hab' noch einen Koffer in Berlin...
>
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