[Cython] Fused Types

[mark florisson]

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().

On the other hand, the user could already do this thing by manually
declaring another fused type that would perhaps be resolved based on
its usage. e.g. for my original example:

ctypedef char *string_t
ctypedef cython.fused_type(int, string_t) attrib_t

cdef func(struct_t mystruct, int i):
    cdef attrib_t var = mystruct.attrib + i

Is this something that should be supported anyway? Currently fused
types can only be used when appearing as argument types (in the
function body and as return value).

>> I'm also wondering if it would be useful to allow actual type
>> retrieval, which could be used in declarations and casts. For instance
>> consider fusing two structs with the same attribute name but different
>> attribute types. Perhaps in your code you want to introduce a variable
>> compatible with such a type, e.g. consider this:
>>
>> ctypdef struct A:
>>    int attrib
>>
>> ctypedef struct B:
>>    char *attrib
>>
>> ctypedef cython.fused_type(A, B) struct_t
>>
>> cdef func(struct_t mystruct, int i):
>>    cdef cython.gettype(mystruct.attrib) var = mystruct.attrib + i
>>    ...
>>
>> What do you think?
>
> Yes, I was thinking that would be supported as well.
>
> - Robert
> _______________________________________________
> cython-devel mailing list
> cython-devel at python.org
> http://mail.python.org/mailman/listinfo/cython-devel
>