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
