Well, not all arrays:
julia> Array{Int}()
0-dimensional Array{Int64,0}:
4544954880
On Wednesday, August 12, 2015 at 11:36:24 AM UTC-4, Mauro wrote:
>
>
>
> On Wed, 2015-08-12 at 17:28, Cedric St-Jean <[email protected]
> <javascript:>> wrote:
> > On Wednesday, August 12, 2015 at 12:15:19 AM UTC-4, Stefan Karpinski
> wrote:
> >>
> >> You can't create a value whose concrete type is Tuple{AbstractString,
> >> AbstractString} but you can create values that are of that type and you
> can
> >> create an instance of Vector{Tuple{AbstractString, AbstractString}}:
> >>
> >> julia> baz(a::Vector{Tuple{AbstractString, AbstractString}}) = 3
> >> baz (generic function with 1 method)
> >>
> >> julia> baz(Vector{Tuple{AbstractString,AbstractString}}())
> >> 3
> >>
> >>
> >>
> > Interesting. Does that really work in 0.4? I tried to replicate in 0.3
> with
> >
> > Vector{(AbstractMatrix,AbstractMatrix)}()
> >> type cannot be constructed
>
> A bit confusingly arrays are not constructed like that:
>
> julia> Vector{Int}()
> ERROR: type cannot be constructed
>
> Instead:
>
> julia> (AbstractMatrix,AbstractMatrix)[]
> 0-element Array{(AbstractArray{T,2},AbstractArray{T,2}),1}
>
> > What kind of object is a Vector{Tuple{AbstractString,AbstractString}}()?
> > Does it have memory allocated to it? What is that construction good for?
>
> It can hold any tuple t for which isa(t, (AbstractMatrix,AbstractMatrix))
> is true. For instance:
>
> julia> push!(a, ([1,2]', speye(3)))
> 1-element Array{(AbstractArray{T,2},AbstractArray{T,2}),1}:
> (
> 1x2 Array{Int64,2}:
> 1 2,
>
> 3x3 sparse matrix with 3 Float64 entries:
> [1, 1] = 1.0
> [2, 2] = 1.0
> [3, 3] = 1.0)
>
>
> Under the hood it is an array of pointers pointing to its entries.
>
> > Cédric
> >
> >
> >>
> >>
> >> On Wed, Aug 12, 2015 at 12:09 AM, Cedric St-Jean <[email protected]
> >> <javascript:>> wrote:
> >>
> >>> Is it correct to say that:
> >>>
> >>> baz(a::Vector{Tuple{AbstractString, AbstractString}}) = 3
> >>>
> >>> is uncallable, since we can't instantiate an AbstractString? Maybe it
> >>> should trigger an error/warning on definition.
> >>>
> >>> Cédric
> >>>
> >>> 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?
> >>>>>>>
> >>>>>>
> >>>>>>
> >>>>
> >>
>
>
