[Cython] Fused Types

[mark florisson]

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

> - Robert
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