Thanks
On Tuesday, March 31, 2015 at 8:49:22 PM UTC+13, Milan Bouchet-Valat wrote:
>
> Le lundi 30 mars 2015 à 18:03 -0700, Steve Cordwell a écrit :
> > Actually there were some bugs in the code. The following code works:
> >
> > zero_mask!{T,N}(a::AbstractArray{T,N}, mask::AbstractArray{Bool,N}) =
> setindex!(a, zero(T), find(!mask))
> >
> > function do_stuff{N}(rows, columns, mask::Nullable{Array{Bool,N}})
> > a = rand(rows, columns)
> > isnull(mask) ? nothing : zero_mask!(a, get(mask))
> > a
> > end
> >
> > do_stuff(rows, columns, mask::Array{Bool}) = do_stuff(rows, columns,
> Nullable(mask))
> >
> > do_stuff(rows, columns) = do_stuff(rows, columns,
> Nullable{Array{Bool}}())
> >
> > However, replacing Array with AbstractArray does not.
> >
> > On Tuesday, March 31, 2015 at 1:23:44 PM UTC+13, Steve Cordwell wrote:
> > Say I want to be able to set the value of an array to zero where
> a boolean mask array is false, then I can define this function:
> >
> > zero_mask!(a::AbstractArray, mask::AbstractArray{Bool}) =
> setindex!(a, zero(T), find(!mask))
> >
> > I have a function that constructs arrays and part of its job is
> to call zero_mask! if a mask is passed to it. I thought I could use
> Nullable types so that there is only one implementation rather than two and
> have helper methods call the do_stuff with the correct arguments.
> >
> > function do_stuff(rows, columns,
> mask::Nullable{AbstractArray{Bool}})
> > a = rand(rows, columns)
> > isnull(mask) ? nothing : zero_mask!(a)
> > a
> > end
> >
> > It would be nice to use do_stuff with just a boolean array,
> rather than specifying it to be Nullable.
> >
> > do_stuff(rows, columns, mask::AbstractArray{Bool}) =
> do_stuff(rows, columns, Nullable(mask))
> >
> > do_stuff(rows, columns) = do_stuff(rows, columns,
> Nullable{AbstractArray{Bool}}())
> >
> > However, I get the following error:
> >
> > do_stuff(10, 3, rand(Bool, 10, 3))
> > ERROR: MethodError: `do_stuff` has no method matching
> do_stuff(::Int64, ::Int64, ::Nullable{Array{Bool,2}})
> >
> > Presumably because I need to define do_study{N}(rows, columns,
> Nullable{Array{Bool,N}}). Is there a way to use Nullable abstract types?
> You're hitting the issue of invariance vs. covariance, about which you
> should be able to find several threads in the archives (but still no
> FAQ?!).
>
> Just use this instead:
> function do_stuff{T<:AbstractArray{Bool}}(rows, columns,
> mask::Nullable{T})
>
>
> Regards
>
