All the getindex implementations should use view, not slice

[jpivarski]

I just noticed that slices copy! They were supposed to be views.

[Moelf]

hmm, I'm pretty sure you're not supposed to make a default slice "view"

JuliaLang/julia#47078

[jpivarski]

This is what I'm seeing, with the concrete Vector class, at least:

julia> original = Vector([1.1, 2.2, 3.3, 4.4, 5.5])
5-element Vector{Float64}:
 1.1
 2.2
 3.3
 4.4
 5.5

julia> sliced = original[2:4]
3-element Vector{Float64}:
 2.2
 3.3
 4.4

julia> viewed = view(original, 2:4)
3-element view(::Vector{Float64}, 2:4) with eltype Float64:
 2.2
 3.3
 4.4

julia> original[3] = 9999
9999

julia> sliced
3-element Vector{Float64}:
 2.2
 3.3
 4.4

julia> viewed
3-element view(::Vector{Float64}, 2:4) with eltype Float64:
    2.2
 9999.0
    4.4

Oh, but maybe this means that the AwkwardArray getindex is correct because it copies, and I should additionally provide a view override.

(In Python, Content instances are considered immutable, so they view everywhere. But AwkwardArray.jl implements Base.push! and Base.append! on its Content instances, so perhaps they should not be presumed immutable. It's also less necessary to require immutability, since typical usage in Julia will be to iterate over arrays, rather than call functions that replace arrays with new arrays.)

[Moelf]

you don't need to add view override yourself. All AbstractArray which has getindex() correctly implemented has view() by default.

You can use @view on one expression, or @views on a whole lexical code block to recover Numpy default slicing