[Cython] Auto-generation of wrapper types

[Schlimbach, Frank]

I like automatism, this one looks useful.

How would you allow extending the Extension type with a new attribute or method? I'd expect that in many cases you need to do more than just wrapping the C class/struct.

-----Original Message-----
From: cython-devel <cython-devel-bounces+frank.schlimbach=intel.com at python.org> On Behalf Of da-woods
Sent: Thursday, March 12, 2020 4:12 PM
To: cython-devel at python.org
Subject: [Cython] Auto-generation of wrapper types

The process of wrapping a C struct or C++ class in an extension type often has the user doing a pretty mechanical duplication of attributes/functions that Cython already knows about. I'm looking at doing:


cdef struct S:

     int a

     # etc.


then `cython.autowrap[S]` would create an extension type that wraps S by value. All attributes convertible to/from a Python type gets a property (as well as any attribute that has an has an autowrap declared). For `cppclass` this would extend to member functions as well - this obviously gets more involved, but again the same basic rule applies of only including stuff with an obvious conversion.

I wouldn't propose to deal with the C++ nightmare of "how to return an owned reference". The idea would be to copy by value or nothing.

I'd also propose only minor customization via keyword arguments (for example the name of a cdef staticmethod constructor, the name of the "obj" field in the C++ class). The basic rule would be that if it doesn't do what you want then it's an extension type, so you can always inherit from it and define the missing bits.

Obviously structs have already have an automatic conversion to/from dicts and some cppclasses have autoconversions too. This wouldn't aim to replace that - it'd just be an option that the user could explicitly ask for.

I have a somewhat working prototype for the struct side. Obviously the real complications are on the C++ side, but I don't think it's hugely difficult providing you accept there's lots of stuff that can't be guessed and inheritance is the way round that.

Does this sound reasonable/something that'd be accepted? Any other thoughts?


David

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