Indexing SArray with SArray of CartesianIndex creates an MArray

[TheBB]

For example (on StaticArrays v0.11)

julia> b = SVector(1);

julia> b[SVector(1)]
1-element SArray{Tuple{1},Int64,1,1}:
 1

julia> b[SVector(CartesianIndex(1))]
1-element MArray{Tuple{1},Int64,1,1}:
 1

Shouldn't this be an SArray?

[c42f]

Similarly, b[SVector{1,UInt8}(1)] returns an MArray; looking at the code at the top of indexing.jl it's a problem with various non-scalar linear indexing which end up in the Base indexing machinery rather than StaticArrays.

[mancellin]

A probably related issue: indexing a Base.Array with a SArray of CartesianIndex returns a different type than indexing the array with a SArray of Int.

julia> A = collect(1:10);

julia> ind = SVector(4, 5, 6);

julia> A[ind]
3-element SVector{3, Int64} with indices SOneTo(3):
 4
 5
 6

julia> ind = SVector(CartesianIndex(4), CartesianIndex(5), CartesianIndex(6));

julia> A[ind]
3-element SizedVector{3, Int64, Vector{Int64}} with indices SOneTo(3):
 4
 5
 6

(StaticArrays v1.0.1, Julia 1.6.0-rc1)

[mateuszbaran]

This probably has the same underlying issue as this: JuliaArrays/HybridArrays.jl#44 (see also JuliaArrays/HybridArrays.jl#41 ). Essentially, indexing things in StaticArrays.jl don't correctly respect arbitrary methods of to_indices. It would be nice to fix it and it shouldn't be hard but it may cause some difficult to predict issues.