Broadcasting style for FillArrays?

[jishnub]

Perhaps we need a broadcasting rule for FillArrays that takes precedence over Broadcast.DefaultArrayStyle{0}. Currently, we obtain the somewhat unsatisfactory

julia> x = Fill(2, 10)
10-element Fill{Int64}, with entries equal to 2

julia> 2 * x * 3
10-element Fill{Int64}, with entries equal to 12

julia> 2 .* x .* 3
10-element Fill{Int64}, with entries equal to 12

julia> @. 2 * x * 3
10-element Vector{Int64}:
 12
 12
 12
 12
 12
 12
 12
 12
 12
 12

This may be resolved by defining a custom broadcast style.

[dlfivefifty]

Note the current approach overloads broadcasted:

FillArrays.jl/src/fillbroadcast.jl

Line 240 in 404fbb5

broadcasted(::DefaultArrayStyle{N}, op, r::AbstractFill{T,N}, x::Number) where {T,N} = Fill(op(getindex_value(r),x), axes(r))

So your second case case works because it's equivalent to broadcasted(*, 2, broadcasted(*, x, 3)) where each one is captured. Probably your third case fails since it is equivalent to broadcasted(*, 2, x, 3) which is not overloaded.

I agree this might be better accomplished with a BroadcastStyle. In particular, many of the other special cases could probably be removed.

[rcalxrc08]

Due to the missing broadcast style it is quite hard to manage interaction with other array packages.

[dlfivefifty]

I agree, but I think someone (other than me, I don't have time) just needs to take the lead on this and make a PR...