"Tuple types are *covariant* in their constituent types"
Ref: http://docs.julialang.org/en/release-0.3/manual/types/#tuple-types
I think this is for the sake of dispatch.
On Wednesday, August 12, 2015 at 2:14:14 PM UTC+2, David Gold wrote:
>
> @Stefan,
>
> I'd have thought that parametric types being invariant in typevars would
> lead to
>
> !(Tuple{ASCIIString, ASCIIString} <: Tuple{String, String})
>
> just as
>
> !(Vector{ASCIIString} <: Vector{String})
>
> Tuples seem to behave specially?
>
> On Tuesday, August 11, 2015 at 4:18:38 PM UTC-4, Stefan Karpinski wrote:
>>
>> Same thing – even though
>>
>> Tuple{ASCIIString,ASCIIString} <: Tuple{String,String} <: Tuple
>>
>>
>> due to invariance, we still have these:
>>
>> !(Vector{Tuple{String,String}} <: Vector{Tuple})
>>
>> !(Vector{Tuple{ASCIIString,ASCIIString}} <: Vector{Tuple})
>> !(Vector{Tuple{ASCIIString,ASCIIString}} <: Vector{Tuple{String,String}})
>>
>>
>> On Tue, Aug 11, 2015 at 4:13 PM, Seth <[email protected]> wrote:
>>
>>> Thanks, Stefan. I understand that causing the problem for baz(), but why
>>> does this explain bar()'s failure?
>>>
>>> On Tuesday, August 11, 2015 at 1:10:27 PM UTC-7, Stefan Karpinski wrote:
>>>>
>>>> Parametric typing in Julia is invariant, so
>>>>
>>>> !(Vector{Tuple{ASCIIString,ASCIIString}} <:
>>>> Vector{Tuple{String,String}})
>>>>
>>>>
>>>> even though
>>>>
>>>> Tuple{ASCIIString,ASCIIString} <: Tuple{String,String}.
>>>>
>>>>
>>>> See:
>>>> http://docs.julialang.org/en/release-0.3/manual/types/#parametric-composite-types
>>>>
>>>> On Tue, Aug 11, 2015 at 1:26 PM, Seth <[email protected]> wrote:
>>>>
>>>>> Consider
>>>>>
>>>>> foo(a::Vector) = 1
>>>>> bar(a::Vector{Tuple}) = 2
>>>>> baz(a::Vector{Tuple{AbstractString, AbstractString}}) = 3
>>>>>
>>>>>
>>>>> foo(a::AbstractString) = foo([(a,a)])
>>>>> bar(a::AbstractString) = bar([(a,a)])
>>>>> baz(a::AbstractString) = baz([(a,a)])
>>>>>
>>>>> Results:
>>>>>
>>>>> julia> foo("a")
>>>>> 1
>>>>>
>>>>> julia> bar("a")
>>>>> ERROR: MethodError: `bar` has no method matching
>>>>> bar(::Array{Tuple{ASCIIString,ASCIIString},1})
>>>>> in bar at none:1
>>>>>
>>>>> julia> baz("a")
>>>>> ERROR: MethodError: `bar` has no method matching
>>>>> bar(::Array{Tuple{ASCIIString,ASCIIString},1})
>>>>> in baz at none:1
>>>>>
>>>>> I understand why foo() works, but why do bar() or baz() both fail?
>>>>>
>>>>
>>>>
>>
