[Cython] Template functions

[Robert Bradshaw]

On Sun, Mar 17, 2013 at 12:15 PM, John Tyree <johntyree at gmail.com> wrote:
>>
>> I was thinking of something along the lines of
>>
>> cdef extern from ...:
>>     cpp_string to_string[T](T value)
>>     T my_func[T, S](T a, S b)
>>     ...
>>
>> It's more a question of how to implement it.
>>
>> - Robert
>
> Well this closely matches the syntax used for classes and won't require any type
> inference, since the user supplies the type at the call site (am I reading that
> correctly?) so I'm not sure what about it will be particularly challenging.
>
> If it's done this way the compiler could generate prototypes as necessary in a
> preprocessing step, without inferring anything about the types until later when
> overloading is resolved. That feels kind of hacky to me, but I've never written
> a compiler with the size and scope of Cython, maybe it's not too bad.  This is
> essentially what the user has to do already, and it "works".
>
> The biggest complaint I have about this method is that without inference it
> looks like it could lead to a *lot* of extra writing out of types. I'm dreading
> the thought of writing out nested template types when calling factory functions
> like those in the thrust library, which was what motivated this in the first
> place.

I think we need something to constrain the argument types (e.g. as
they relate to each other), as well as provide a return type. The
"any" type seems to lead way to easily to incorrect code, as well as
surprises, e.g. is the "object" type accepted? (FWIW, I was thinking
of allowing inference, that'll actually be pretty easy once the rest
is in place.)

- Robert