Strides on when SubArray has a scalar sub index

[Tokazama]

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I've been getting incorrect results when using scalar indexing that doesn't start with one on views.

julia> A = zeros(3, 4, 5);

julia> A[:] = 1:60;

julia> Aview = view(A, :, 2, :);

julia> ArrayInterface.StrideIndex(Aview)[1,1]
1

julia> Aview[1,1]
4.0

julia> Aview = view(A, 2, :, :);

julia> ArrayInterface.StrideIndex(Aview)[1,1]
1

julia> Aview[1,1]
2.0

Should we be combining those scalar indices with strides?

[chriselrod]

julia> A = zeros(3, 4, 5);

julia> A[:] = 1:60;

julia> Aview = view(A, :, 2, :);

julia> ArrayInterface.StrideIndex(Aview)[1,1]
1

julia> Aview[ArrayInterface.StrideIndex(Aview)[1,1]]
4.0

julia> Aview[1,1]
4.0

What's the desired behavior here? I guess (for efficiency), that it returns a linear index into the memory of the array?

In that case, the StrideIndex object should carry an offset. The offset should default to Zero() for most array types, for subarrays should be calculated using the offsets implied by the non-colon indices. E.g., (2 - offset(A,2)) * stride(A,2) for the first example, and (2 - offset(A,1)) * stride(A,1) for the second.

[chriselrod]

Also, methods like pointer do the offsetting for you:

julia> using ArrayInterface

julia> A = zeros(3, 4, 5);

julia> A[:] = 1:60;

julia> Aview = view(A, :, 2, :);

julia> unsafe_load(pointer(Aview), ArrayInterface.StrideIndex(Aview)[1,1])
4.0

julia> Aview[1,1]
4.0

julia> Aview = view(A, 2, :, :);

julia> unsafe_load(pointer(Aview), ArrayInterface.StrideIndex(Aview)[1,1])
2.0

julia> Aview[1,1]
2.0