[C++-sig] virtual functions with default implementation

[Stefan Seefeld]

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

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