[Cython] Fused Types

[Robert Bradshaw]

On Tue, May 3, 2011 at 12:59 AM, mark florisson
<markflorisson88 at gmail.com> wrote:
> On 3 May 2011 00:21, Robert Bradshaw <robertwb at math.washington.edu> wrote:
>> On Mon, May 2, 2011 at 1:56 PM, mark florisson
>> <markflorisson88 at gmail.com> wrote:
>>> On 2 May 2011 18:24, Robert Bradshaw <robertwb at math.washington.edu> wrote:
>>>> On Sun, May 1, 2011 at 2:38 AM, mark florisson
>>>> <markflorisson88 at gmail.com> wrote:
>>>>> A remaining issue which I'm not quite certain about is the
>>>>> specialization through subscripts, e.g. func[double]. How should this
>>>>> work from Python space (assuming cpdef functions)? Would we want to
>>>>> pass in cython.double etc? Because it would only work for builtin
>>>>> types, so what about types that aren't exposed to Python but can still
>>>>> be coerced to and from Python? Perhaps it would be better to pass in
>>>>> strings instead. I also think e.g. "int *" reads better than
>>>>> cython.pointer(cython.int).
>>>>
>>>> That's whey we offer cython.p_int. On that note, we should support
>>>> cython.astype("int *") or something like that. Generally, I don't like
>>>> encoding semantic information in strings.
>>>>
>>>> OTHO, since it'll be a mapping of some sort, there's no reason we
>>>> can't support both. Most of the time it should dispatch (at runtime or
>>>> compile time) based on the type of the arguments.
>>>
>>> If we have an argument type that is composed of a fused type, would be
>>> want the indexing to specify the composed type or the fused type? e.g.
>>>
>>> ctypedef floating *floating_p
>>
>> How should we support this? It's clear in this case, but only because
>> you chose good names. Another option would be to require
>> parameterization floating_p, with floating_p[floating] the
>> "as-yet-unparameterized" version. Explicit but redundant. (The same
>> applies to struct as classes as well as typedefs.) On the other had,
>> the above is very succinct and clear in context, so I'm leaning
>> towards it. Thoughts?
>
> Well, it is already supported. floating is fused, so any composition
> of floating is also fused.
>
>>> cdef func(floating_p x):
>>>    ...
>>>
>>> Then do we want
>>>
>>>    func[double](10.0)
>>>
>>> or
>>>
>>>    func[double_p](10.0)
>>>
>>> to specialize func?
>>
>> The latter.
>
> I'm really leaning towards the former.

Ugh. I totally changed the meaning of that when I refactored my email.
I'm in agreement with you: func[double].

> What if you write
>
> cdef func(floating_p x, floating_p *y):
>    ...
>
> Then specializing floating_p using double_p sounds slightly
> nonsensical, as you're also specializing floating_p *.
>
>>> FYI, the type checking works like 'double_p is
>>> floating_p' and not 'double is floating_p'. But for functions this is
>>> a little different. On the one hand specifying the full types
>>> (double_p) makes sense as you're kind of specifying a signature, but
>>> on the other hand you're specializing fused types and you don't care
>>> how they are composed -- especially if they occur multiple times with
>>> different composition. So I'm thinking we want 'func[double]'.
>>
>> That's what I'm thinking too. The type you're branching on is
>> floating, and withing that block you can declare variables as
>> floating*, ndarray[dtype=floating], etc.
>
> What I actually meant there was "I think we want func[double] for the
> func(floating_p x) signature".
>
> Right, people can already say 'cdef func(floating *p): ...' and then
> use 'floating'. However, if you do 'cdef floating_p x): ...', then
> 'floating' is not available, only 'floating_p'. It would be rather
> trivial to also support 'floating' in the latter case, which I think
> we should,

floating is implicitly available, we could require making it explicit.

> unless you are adamant about prohibiting regular typedefs
> of fused types.

No, I'm nto adamant against it, just wanted to get some discussion going.

- Robert