[Cython] Fused Types

[mark florisson]

On 28 April 2011 23:59, Robert Bradshaw <robertwb at math.washington.edu> wrote:
> On Thu, Apr 28, 2011 at 2:29 PM, mark florisson
> <markflorisson88 at gmail.com> wrote:
>> On 28 April 2011 22:31, mark florisson <markflorisson88 at gmail.com> wrote:
>>> On 28 April 2011 22:12, Robert Bradshaw <robertwb at math.washington.edu> wrote:
>>>> On Thu, Apr 28, 2011 at 12:48 PM, mark florisson
>>>> <markflorisson88 at gmail.com> wrote:
>>>>
>>>>> So I fixed all that, but I'm currently wondering about the proposed
>>>>> cython.typeof(). I believe it currently returns a string with the type
>>>>> name, and not the type itself.
>>>>
>>>> Yes. This is just because there's not really anything better to return
>>>> at this point. We should "fix" this at some point in the future.
>>>>
>>>>> So I think it would be inconsistent to
>>>>> suddenly start allowing comparison with 'is' and 'isinstance' and
>>>>> such.
>>>>
>>>> I'm open to other suggestions, but would like an expression that
>>>> resolves at compile time to true/false (and we need to do branch
>>>> pruning on it). Note that type() is not good enough, because it has
>>>> different semantics, i.e.
>>>>
>>>>    cdef object o = []
>>>>    typeof(o), type(o)
>>>>
>>>> so lets not touch that one.
>>>
>>> Right, so for fused types I don't mind string comparison with
>>> cython.typeof(), but retrieval of the actual type for casts and
>>> declaration remains open. I'd be fine with something like
>>> cython.gettype().
>>
>> It seems that this isn't optimized yet, but it looks to me like it
>> wouldn't be very hard to do so. At least == and != could be resolved
>> at compile time if the other operand is a string literal.
>
> Yes. We could consider supporting "typeof(x) is typeof(double)" or
> even "typeof(int*)" etc. as well to not tie ourselves to strings. Or
> perhaps some other syntax we haven't thought of. Alternatively, it
> would be nice if it involved the literal fused_type as that's what
> we're really branching on, e.g.
>
> ctypedef cython.fused_type(A, B) AorB
>
> cdef foo(AorB x):
>    if AorB[A]:   # or .A or something
>        ...
>
> it's hard to come up with something that plays nicely with pointer types.

I like the typeof(my_type_here). So if we support listing types in
typeof(), then you could also call typeof() on AorB to specialize.

> - Robert
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