Can you provide a Foo example of how this works, with both construction and
method definition?
On Wednesday, December 9, 2015 at 9:32:36 AM UTC-5, Yichao Yu wrote:
>
> On Wed, Dec 9, 2015 at 9:22 AM, milktrader <milkt...@gmail.com
> <javascript:>> wrote:
> > I'd like a somewhat clever example (or boring one for that matter) that
> > shows:
> >
> > 1. How to create an instance of a singleton type
>
> Call the constructor just like any other types.
>
> The only special thing about singleton type is that two instance of a
> mutable singleton type are identical. Other than this, they are simply
> types that doesn't have a field.
>
> >
> > 2. How to write methods that use this type in a meaningful way.
>
> Just like any other types. As long as you are not comparing them, they
> are exactly the same with everything else.
>
> >
> > 3. How it's used in Base code (I seem to recall Void is a singleton
> type)
> >
> > On Wednesday, December 9, 2015 at 9:02:31 AM UTC-5, tshort wrote:
> >>
> >> I'm not sure what you want, either. How about this?
> >>
> >> julia> type BadInt{X} end
> >>
> >> julia> BadInt{3}()
> >> BadInt{3}()
> >>
> >> julia> f{X}(::Type{BadInt{X}}, y) = X - y
> >> f (generic function with 1 method)
> >>
> >> julia> f(BadInt{10}, 3)
> >> 7
> >>
> >> julia> f{X}(::BadInt{X}, y) = X - y
> >> f (generic function with 2 methods)
> >>
> >> julia> f(BadInt{10}(), 3)
> >> 7
> >>
> >>
> >> On Wed, Dec 9, 2015 at 8:56 AM, Eric Forgy <eric....@gmail.com> wrote:
> >>>
> >>> Not sure I follow, but does this help?
> >>>
> >>> julia> type BadInt
> >>> end
> >>>
> >>> julia> bi = BadInt()
> >>> BadInt()
> >>>
> >>> julia> typeof(bi)
> >>> BadInt
> >>>
> >>>
> >>> On Wednesday, December 9, 2015 at 9:46:01 PM UTC+8, milktrader wrote:
> >>>>
> >>>> How do you create an instance of type BadInt then?
> >>>>
> >>>> On Wednesday, December 9, 2015 at 7:01:25 AM UTC-5, milktrader wrote:
> >>>>>
> >>>>> Trying to wrap my mind around singleton types to see if they might
> be
> >>>>> useful for something I'm working on, but running into some
> confusion. Here
> >>>>> is an example that I started working with:
> >>>>>
> >>>>> julia> type BadInt
> >>>>> end
> >>>>>
> >>>>> julia> import Base.+
> >>>>>
> >>>>> julia> +(x::BadInt, y::Int64) = x - y
> >>>>> + (generic function with 172 methods)
> >>>>>
> >>>>> julia> BadInt() = 2
> >>>>> BadInt
> >>>>>
> >>>>> julia> BadInt + 2
> >>>>> ERROR: MethodError: `+` has no method matching +(::Type{BadInt},
> >>>>> ::Int64)
> >>>>> Closest candidates are:
> >>>>> +(::Any, ::Any, ::Any, ::Any...)
> >>>>> +(::Int64, ::Int64)
> >>>>> +(::Complex{Bool}, ::Real)
> >>>>> ...
> >>>>>
> >>>>> As I understand, a singleton type can only take on a single value.
> >>>>> What's the utility in supporting this?
> >>
> >>
> >
>
