view != getindex, with IdentityUnitRange

[mcabbott]

I got some strange results copying a piece into a larger array, and if I understand right it looks like a problem with how view deals with IdentityUnitRange.

julia> out = reshape(1:15, 5,3) .+ 0; 

julia> item1 = 101:100:301;

julia> out[axes(item1)..., 1] .= item1; 

julia> out 
5×3 Array{Int64,2}:
 101   6  11
 201   7  12
 301   8  13
   4   9  14
   5  10  15

julia> item = OffsetArray(102:100:302, +2)
102:100:302 with indices 3:5

julia> out[axes(item)..., 1] # looks correct  
3-element OffsetArray(::Array{Int64,1}, 3:5) with eltype Int64 with indices 3:5:
 301
   4
   5

julia> view(out, axes(item)..., 1) # wrong? 
3-element view(::Array{Int64,2}, :, 1) with eltype Int64 with indices 3:5:
 5
 6
 7

julia> out[axes(item)..., 2] .= item;

julia> copyto!(view(out, axes(item)..., 2), item); # same effect

julia> out # values of item are in the wrong places!
5×3 Array{Int64,2}:
 101    6  202
 201    7  302
 301    8   13
   4    9   14
   5  102   15

(@v1.5) pkg> st OffsetArrays
Status `~/.julia/environments/v1.5/Project.toml`
  [6fe1bfb0] OffsetArrays v0.11.4

[johnnychen94]

If you wrap it with CartesianIndices, it works as expected...

julia> view(out, CartesianIndices(item), 1)
3-element view(::Array{Int64,2}, [3, 4, 5], 1) with eltype Int64:
 301
   4
   5

julia> to_indices(item, (axes(item)..., 1))
(3:5, 1)

julia> to_indices(item, (CartesianIndices(item), 1))
(CartesianIndex{1}[CartesianIndex(3,), CartesianIndex(4,), CartesianIndex(5,)], 1)

[mcabbott]

Thanks, that's a useful work-around, which I would never have thought to try!

[johnnychen94]

update with another result:

julia> ind = OffsetArrays.IdOffsetRange(3:5, 0)
3:5

julia> view(out, ind, 1)
3-element view(::Array{Int64,2}, 3:5, 1) with eltype Int64 with indices 3:5:
 5
 6
 7

julia> view(out, 3:5, 1)
3-element view(::Array{Int64,2}, 3:5, 1) with eltype Int64:
 301
   4
   5

Definitely that there's something not covered here. Let me see if I can tackle this ( seems like a good exercise to me :P)

[johnnychen94]

For the usage of OffsetArrays, this issue is fixed by #101

As @timholy indicated, we should also give a patch in Base so that other types of index-preserving ranges don't need such a fix. Hence I'll keep this issue open until I find some time for that.