make setindex with colon fall back to fill!

[KristofferC]

Update to #13459. Fixes #16302 for Arrays. @mbauman mentioned in #13459 (comment) that this could be extended to AbstractArray but that it has the extra complication of dealing with the vararg call.

For now, this at least improves the situation for Arrays as compared to the results in #16302.

julia> function foo(A)
           for i = 1:10^6
               A[:] = 0
           end
       end
foo (generic function with 1 method)

julia> @time foo([3,4,5])
  0.005799 seconds (5 allocations: 272 bytes)

cc @stevengj

[stevengj]

Note that the {T} is not necessary here. Note also that you don't need to name the c argument since it is never used.

What is the problem with just doing setindex!(A::AbstractArray, x::Number, ::Colon) = fill!(A, x)?

[stevengj]

Or even more generally:

setindex!{T}(A::AbstractArray{T}, x::Union{Number,T}, ::Colon) = fill!(A, x)

[mbauman]

Defining it on setindex! directly for all AbstractArrays leads to nasty ambiguity issues when custom arrays want to define their own behaviors. They'll want to define a method with a more specific array type but less specific value and index types.

Interestingly, this is a new and exciting way for Base to break packages.

[KristofferC]

I will try out your suggestions.

[KristofferC]

Your suggested Union does not seem to do the intended overloading @stevengj :

julia> import Base.setindex!

julia> A = rand(3,3);

julia> @which A[:] = 0
setindex!(A::AbstractArray, v, I...) at abstractarray.jl:498

julia> setindex!{T}(A::Array{T}, x::Union{Number,T}, ::Colon) = fill!(A, x)
setindex! (generic function with 90 methods)

julia> @which A[:] = 0
setindex!(A::AbstractArray, v, I...) at abstractarray.jl:498

julia> setindex!{T}(A::Array{T}, x::Number, ::Colon) = fill!(A, x)
setindex! (generic function with 91 methods)

julia> @which A[:] = 0
setindex!{T}(A::Array{T,N<:Any}, x::Number, ::Colon) at REPL[8]:1

[mbauman]

Oh, yeah, that's #3738 (unions with static type parameters are problematic). Julia can either match the second argument to the Number in the union, or it can bind T to Int and match the typevar. Julia chooses poorly.

[mbauman]

If you want to allow all non-array values, you need two methods:

setindex!(A::Array, X::AbstractArray, ::Colon) = # manual loop
setindex!(A::Array, x, ::Colon) = fill!(A, x)

[tkelman]

Why was this decided against last time it came up?

[yuyichao]

This was proposed as a fix to a worse issue which we had a better solution of. It wasn't clear that the splatting issue is this bad I guess.