I will likely do so, it's quite a common action to take.
Fortunately with typeof( ( 1,2 ) ) == Tuple{Int64,Int64} there is a
significantly greater consistency in 0.4 vs 0.3
Though how would one correctly access the 'nth' elements type ?
It brings up a question regarding parameterized types, how should (or
should) one access/refer to the parameters of the type rather than an
instance. It seems like a bad (queezy) practice to dig into the parameters
of a type?
On Thursday, September 3, 2015 at 9:41:18 AM UTC-4, Tim Holy wrote:
>
> base/dict.jl defines keytype and valtype, but they are not exported. You
> could
> file a pull request that exports them (it would be a 2-line patch, though
> you
> might want to add a test to make sure they stay exported).
>
> --Tim
>
> On Thursday, September 03, 2015 06:37:02 AM Michael Francis wrote:
> > In the short term I have defined the following in the offending package
> for
> > v0.4 only
> >
> > function keytype( dict )
> > return eltype( dict ).parameters[1]
> > end
> >
> > I agree that a standard protocol of accessing the key and value types of
> a
> > pair / associative is the way to go.
> >
> > On Thursday, September 3, 2015 at 9:31:39 AM UTC-4, Matt Bauman wrote:
> > > Oh man that's tricky. The trouble is that you're effectively saying
> > > `Pair{Symbol,Int}[1]`, which is the syntax for a typed array:
> > > Pair{Symbol,Int}[:x=>1, :y=>2]. One way around this is to define:
> > >
> > > keytype{A,B}(::Type{Pair{A,B}}) = A
> > > valuetype{A,B}(::Type{Pair{A,B}}) = B
> > > pairtypes{A,B}(::Type{Pair{A,B}}) = (A,B)
> > >
> > > If you need this to work on 0.3, too, you can easily make these
> functions
> > > work for the old-style Tuples, too.
> > >
> > > On Thursday, September 3, 2015 at 9:06:30 AM UTC-4, Michael Francis
> wrote:
> > >> Incidentally
> > >>
> > >> eltype( Pair{String,Float64} )
> > >>
> > >> gives Any, that seems slightly strange as well .
> > >>
> > >> On Thursday, September 3, 2015 at 9:02:33 AM UTC-4, Michael Francis
> wrote:
> > >>> julia> eltype( Dict( :x => 1, :y => 2 ) )[1]
> > >>> ERROR: MethodError: `convert` has no method matching
> convert(::Type{Pair
> > >>> {Symbol,Int64}}, ::Int64)
> > >>> This may have arisen from a call to the constructor
> Pair{Symbol,Int64
> > >>> }(...),
> > >>> since type constructors fall back to convert methods.
> > >>>
> > >>> Closest candidates are:
> > >>> Pair{A,B}(::Any, ::Any)
> > >>> call{T}(::Type{T}, ::Any)
> > >>> convert{T}(::Type{T}, ::T)
> > >>>
> > >>> in getindex at array.jl:167
> > >>>
> > >>> Is this intentional ? This breaks a package I am dependent on - I
> > >>> believe the assumption was that Pair would respect the tuple API,
> this
> > >>> appears to not be the case ?
> > >>>
> > >>> collect( eltype( Dict( :x => 1, :y => 2 ) ) )
> > >>> ERROR: MethodError: `start` has no method matching
> start(::Type{Pair{
> > >>> Symbol,Int64}})
> > >>>
> > >>> in collect at array.jl:255
> > >>> in collect at array.jl:262
>
>
