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
>>>
>>>
>>>
