%2B%2B-SIG ----- Original Message -----
From: "Ralf W. Grosse-Kunstleve" <rwgk@[...].com> 
To: <c++-sig@[...].org> 
Sent: Monday, July 15, 2002 12:14 PM
Subject: Re: [C++-sig] extractors


>  --- David Abrahams <david.abrahams@[...].com> wrote:
>  >     d. Ultimately, that means that if the overload succeds, but the
>  > iterable contains the wrong kind of elements, the selected function
itself
>  > will appear (from the Python side) to throw an exception immediately.
That
>  > seems acceptable to me.
> 
>  The tests that go with my prototype implementation of the sequence ->
container
>  converter include a test for these overloads:
> 
>    int boost_array_3(boost::array<double, 3> const& a);
>    int boost_array_4(boost::array<double, 4> const& a);
> 
>      .def("boost_array", boost_array_3)
>      .def("boost_array", boost_array_4)
> 
>  For this to work as expected the convertible() test has to know the
number of
>  elements in the sequence. Is this possible if the input sequence can only
be
>  traversed once?

If it exposes a __len__ method, I think the answer is yes ;-)

>  Ideas:
> 
>  a. I could simply limit the boost::array converters to lists and tuples.
In our
>  environment this would be fully sufficient.

I think it would be fine to limit them to iterables with __len__ methods.
List and tuple both fall into this category.

>  b. Or, if the input Python object is a list or tuple I check the length.
>  Otherwise convertible() returns true and construct() throws an exception
if the
>  sequence length is not compatible.

Whether or not this is acceptable/appropriate really depends on the users'
needs. Since you guys are the users, I guess I have no comment.

>  c. Extending the idea: if the input Python object is a list or tuple I
check
>  both the length and the convertibility of each element. For any other
sequence
>  convertible() returns true and construct() throws an exception if there
is a
>  problem.

I think the real, deep answers to this lie somewhere in PEP 246:

http://www.python.org/peps/pep-0246.html


-Dave