[Cython] Auto-generation of wrapper types

[Stefan Behnel]

da-woods schrieb am 12.03.20 um 16:11:
> 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.

Sounds like a good idea in general. Questions:

What makes C structs and C++ classes special enough to make this a separate
language feature? That should be part of a motivation somewhere (probably
in a ticket).

How does this relate to the support for @dataclass in GH-2903? Is the only
difference that you would write "x.member" instead of "x.structattr.member"?

https://github.com/cython/cython/issues/2903

Why "autowrap[S]" and not "autowrap(S)"? I'm asking also because there
should probably be a way for this to work in Python files, for which a
function call seems more natural.

It also feels like a @decorator would somehow fit quite well here. Even
when defined in a .pxd file, the struct would still only be exported in the
corresponding module (with the same name). Something like this:

    @cclass
    cdef struct S:
        int x

Not sure if reusing @cclass is a good idea, but it doesn't seem wrong.

Defining this in a .pxd file could then even allow cimporting modules to
understand the extension type wrapper as well, by simply reconstructing the
type representation on their side.

Stefan