[Cython] Declaration syntax change

[Nathaniel Smith]

On Thu, Oct 3, 2013 at 1:23 PM, Stefan Behnel <stefan_ml at behnel.de> wrote:
> Greg Ewing, 03.10.2013 14:10:
>> Robert Bradshaw wrote:
>>>     cdef int *a, b, c, *d[3]
>>>
>>> is IMHO quite ugly but also adds a lot of complexity to the parser.
>>> What if instead we required
>>>
>>>     cdef int* a
>>>     cdef int b, c
>>>     cdef int[3]* d
>
> The last line looks ambiguous, BTW, hadn't even noticed it before. Is that
> an array of int pointers or a pointer to an array (pointer)? We should make
> sure the way this is declared is really obvious and not unexpected to C users.
>
>
>> What would be the benefit of this? You're proposing to change
>> from something identical to C declaration syntax, which is
>> second nature for a great many people, to something that
>> looks deceptively like C syntax but isn't.
>
> The reasoning is that the C syntax is error prone and less readable than it
> could be, because you have to spot stars in the right places of a
> potentially long list of variable names to know if something is a value or
> a pointer. If there was only one type declaration, right after the cdef, it
> would be much clearer. It would just say: "this is a list of variables
> declared as int*", not mixing any further types into it.
>
> Also, C is only second nature to some people. A great many people actually
> use Cython specifically to *avoid* having to write C.

The two halves of this email seem to sort of contradict each other,
don't you think? At least the C syntax has the advantage that it's
well-defined and many people *do* know it (and if they don't then
there are bazillions of references around, plus you can just copy it
out of header files if you're wrapping a C library), whereas as noted
above, in fact there are *no* people who know how to look at int[3]*
and be confident about what it means, even you...?

(I'm not against improving on C in general, but I'm far from convinced
that there's any syntax for encoding C types that's sufficiently
better than what C does to be worth the switching costs.)

If what really bothers you is having objects of different types
declared within the same statement then you could just litigate *that*
out of existence directly... not convinced this would be worthwhile
(though I do tend to use that style myself already), but it seems more
viable than trying to reinvent C's type syntax.

-n