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
