On Fri, Oct 28, 2016 at 12:07 PM, Derek Gaston <fried...@gmail.com> wrote:
> I can't quite seem to get the right syntax for creating methods that are
> keyed off of subtypes (as a parameter).
>
> Say I have:
>
> abstract foo
> abstract bar <: foo
>
> I want to create a function that is like so:
>
> function doStuff(::Type{foo})
> end
>
> in such a way that I can call it with "Type{bar}". i.e.:
> doStuff(Type{bar})
>
> I understand that:
>
> # Returns true:
> issubtype(bar, foo)
>
> # Returns false:
> issubtype(Type{bar}, Type{foo})
>
> And I understand why.
>
> So... I tried to define:
>
> function doStuff{T}(::Type{T<:foo})
> end
>
> But it tells me that: "WARNING: static parameter T does not occur in
> signature" (it looks like it does to me! :-)... so that's not the right
> answer.
>
function doStuff{T <: foo}(::Type{T})
end
>
> Obviously I'm just thinking about the problem incorrectly... so can
> someone shed some light on what's up here?
>
> Before you ask: I really do need to operate on the _types_ and not on
> instances of the objects themselves (which would obviously be
> straightforward to do).
>
>
>
>
> Also: a (related) follow-on question. What is the correct/preferred way
> to do the following:
>
> function createSomething{T}()
> return T()
> end
>
>
If you want to implement the "factory pattern", that can be simulated, but
I'm not sure it's necessary (or useful) in Julia.
See also:
http://stackoverflow.com/a/35524338/508431
http://docs.julialang.org/en/latest/manual/constructors/#out
er-constructor-methods
(obviously, this is a toy example, my real application of this is not
> trivial)
>
> Is it to do:
>
> function createSomething{T}(::Type{T})
> return T()
> end
>
> ?
>
>
>
>
> Thanks for any help!
>
> Derek
>
