On Nov 24, 2009, at 11:51 PM, Stefan Behnel wrote:
> Robert Bradshaw, 25.11.2009 04:27:
>> On Nov 24, 2009, at 1:18 PM, Lisandro Dalcin wrote:
>>>> Joachim Saul, 24.11.2009 20:59:
>>>>> cdef extern from "Python.h":
>>>>> ctypedef class __builtin__.str [object PyStringObject]:
>>>>> pass
>>>
>>> Anyway, any good reason for such code to fail in Cython? Should we
>>> support such declarations of builtin types? I think Cython should be
>>> able to compile as much Pyrex code as possible.
>>
>> I agree, it shouldn't fail (though perhaps there should be a
>> warning).
>> The underlying issue is that it doesn't recognize that the user-
>> declared type could be compatible with the builtin type. We should
>> recognize this and allow it.
>
> I disagree. This would either require us to check the declaration
> exactly
> (in which case there would be zero gain at all, as Cython would need
> to
> know the complete type declaration already), or it would allow users
> to
> declare all sorts of broken things on the type without checking. The
> latter
> means that there could be all sorts of surprises for users that see
> their
> code work or fail, depending on what they think they have declared.
I'm proposing something much simpler--if the name matches for a
__builtin__ type, we allow assignment. If the extern declaration is
erroneous, that will break things, but that's *always* the case with
extern declarations. In general, a gcc error means check your extern
declarations. (We should warn that a builtin type is being overridden.)
> I think the right way to handle this would be to finish up subtyping
> support and type fields for builtin types (IIRC, that's what's still
> missing?),
Yes, we should do this (though I'm doubtful the public and private
APIs are all consistent from 2.3-3.x).
> and then emit either an error on the above, or a clear warning
> that states that the senseless redefinition of a builtin type has been
> ignored (which IMHO is a very good argument for making it an error).
The users type declaration would not be ignored, it would override the
builtin one, just like
cdef extern from *:
cdef object range(object)
would override the builtin range.
- Robert
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