On Friday, 29 May 2015 10:37:38 UTC-3, Yichao Yu wrote:
>
> On Fri, May 29, 2015 at 9:21 AM, andrew cooke <[email protected]
> <javascript:>> wrote:
> >
> > Ahh!
> >
> > No, its possible:
> >
> >
> > julia> foo(::Nullable{Union()}) = "empty"
> > foo (generic function with 1 method)
> >
> > julia> foo(::Nullable{Int}) = "int"
> > foo (generic function with 2 methods)
> >
> > julia> foo(Nullable())
> > "empty"
> >
> > julia> foo(Nullable(4))
> > "int"
>
> I'm not sure if this is what you want.
>
> The point of Nullable is that it maintains type stability when you
> return "missing value", i.e. the type of a Nullable you should get
> from a function should always be the same (otherwise there's no point
> to use Nullable to begin with).
can you expand on this? what if i'm writing some code that constructs
arbitrary types, and i need to know whether the user constructed
"anything", or decided to not do so on this call. wouldn't that be a
suitable use of Nullable{Any}?
In a function that returns Int or a
> missing value, you return either Nullable(<int value>) or
> Nullable{Int}().
>
> Unfortunately, this means that you cannot dispatch on the type (since
> there's only one and that's the point). IMHO, depending on your
> usecase, you might be better off branching on whether the Nullable has
> a value.
>
> >
> >
> > Sorry, please ignore!
>
