[C++-sig] Calling python from c++ with tuple and dict args.

[David Abrahams]

Alex Mohr <amohr at pixar.com> writes:

>> not 
>> 
>>    o(A1..N, unpacked_dict_args)
>> 
>> as well?
>
> Yes -- that too, and that's what I've implemented.
>
>> That won't work with the old broken compilers (vc6/7), I think, which
>> -- at least for now -- are still supported.  But I think it's pretty
>> easy to do something inside boost/python/call.hpp to make it recognize
>> the unpacked tuple and dict arguments and treat them specially.
>
> Interesting.  The only environments I have readily available are gcc 4+ 
> on linux and vc-8_0 on Windows and the obvious thing seems to work on 
> those.  So I'll likely need some help with supporting the older 
> compilers.  Or -- is there an existing pattern somewhere that I can look at?

Just don't rely on partial ordering or partial specialization.  Detect
the special types inside of each call<> overload using type traits and
handle them appropriately using some kind of metaprogramming.

>> If you just modify boost::python::call<> you don't need to touch
>> anything else.
>
> That's true -- I'll do that.  There is the question of whether 
> unpacked_tuple and unpacked_dict should count against MAX_ARITY though. 
>   That is, is MAX_ARITY the max number of explicit positional args, or 
> is MAX_ARITY the max number of c++ args?

Make it the latter; it will be simpler.

> What is the preferred way of generating a patch to post to the list?

_enclose_ (rather than paste) a unified diff into a post.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com