[Pyrex] External functions and extension types: Was: Please support C++

[Greg Ewing]

Lenard Lindstrom wrote:

> I was wondering if any decision has been made as to how external 
> functions returning extension types will be handled.

No firm decision yet, but I'm thinking about a scheme
which will track both the logical type and the actual
declared C type of all expressions. This would open
up flexibility for future policy decisions on such
things as whether all temporary variables are declared
as PyObject * or not, and a possible "split" type
declaration syntax for handling the above problem.

> What is not handled is the case where a function is logically defined 
> to return 'object' but in fact returns something else in the .h file.

I don't see what you would gain by declaring it that
way, rather than making the Pyrex declaration match
the actual declaration.

> The plan is to always C cast the return value of an external 
> function returning a Python object but not functions defined in 
> Pyrex.

That may serve as an interim solution, but I wouldn't
like it to be made permanent. Ultimately I'd like a
scheme in which Pyrex always knows exactly how everything
is declared and acts accordingly.

> If a special declaration is to be used then may I suggest something 
> like this:
> 
> cdef extern from "something.h":
>     cdef class EXTTYPE ...
>     cdef <EXTTYPE> somefunc(...)

I'm currently thinking of something like

     cdef <object> MyType somefunc(...)

so you get to be explicit about both the logical and
actual type. Have to think more about how to weave this
into C's inside-out type declaration syntax, though.

 > But I do not wish to explore this any further until
 > a decision is made.

You're not likely to get any definitive decisions about
this until I actually release the next version, since
I won't really know whether what I'm thinking of is
workable until I've tried to implement it.

I probably won't be using any of your patches as-is
anyway. Not that I don't appreciate your efforts, but
I feel I need to keep a firm grip on the overall design,
or it will all turn to custard...

-- 
Greg Ewing, Computer Science Dept, +--------------------------------------+
University of Canterbury,	   | A citizen of NewZealandCorp, a	  |
Christchurch, New Zealand	   | wholly-owned subsidiary of USA Inc.  |
greg.ewing at canterbury.ac.nz	   +--------------------------------------+