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Treat zero-dimensional views as contiguous SubArrays #29895

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Nov 2, 2018
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Treat zero-dimensional views as contiguous SubArrays #29895

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9 changes: 6 additions & 3 deletions base/subarray.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -46,7 +46,7 @@ check_parent_index_match(parent, ::NTuple{N, Bool}) where {N} =
throw(BoundsError(T(parent, indices, offset1, stride1), I))

# This computes the linear indexing compatibility for a given tuple of indices
viewindexing() = IndexLinear()
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The function viewindexing() is never called without an argument in Base, so I assume this line was meant as the fallback case for viewindexing(tail(I)). Changing the argument to an empty tuple provides the correct linear indexing if all indices are ScalarIndex.

viewindexing(I::Tuple{}) = IndexLinear()
# Leading scalar indices simply increase the stride
viewindexing(I::Tuple{ScalarIndex, Vararg{Any}}) = (@_inline_meta; viewindexing(tail(I)))
# Slices may begin a section which may be followed by any number of Slices
Expand Down Expand Up @@ -236,8 +236,10 @@ function getindex(V::FastSubArray, i::Int)
@inbounds r = V.parent[V.offset1 + V.stride1*i]
r
end
# We can avoid a multiplication if the first parent index is a Colon or AbstractUnitRange
FastContiguousSubArray{T,N,P,I<:Tuple{Union{Slice, AbstractUnitRange}, Vararg{Any}}} = SubArray{T,N,P,I,true}
# We can avoid a multiplication if the first parent index is a Colon or AbstractUnitRange,
# or if all the indices are scalars, i.e. the view is for a single value only
FastContiguousSubArray{T,N,P,I<:Union{Tuple{Union{Slice, AbstractUnitRange}, Vararg{Any}},
Tuple{Vararg{ScalarIndex}}}} = SubArray{T,N,P,I,true}
function getindex(V::FastContiguousSubArray, i::Int)
@_inline_meta
@boundscheck checkbounds(V, i)
Expand Down Expand Up @@ -283,6 +285,7 @@ stride(V::SubArray, d::Integer) = d <= ndims(V) ? strides(V)[d] : strides(V)[end
compute_stride1(parent::AbstractArray, I::NTuple{N,Any}) where {N} =
(@_inline_meta; compute_stride1(1, fill_to_length(axes(parent), OneTo(1), Val(N)), I))
compute_stride1(s, inds, I::Tuple{}) = s
compute_stride1(s, inds, I::Tuple{Vararg{ScalarIndex}}) = s
compute_stride1(s, inds, I::Tuple{ScalarIndex, Vararg{Any}}) =
(@_inline_meta; compute_stride1(s*unsafe_length(inds[1]), tail(inds), tail(I)))
compute_stride1(s, inds, I::Tuple{AbstractRange, Vararg{Any}}) = s*step(I[1])
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3 changes: 3 additions & 0 deletions test/subarray.jl
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Expand Up @@ -619,3 +619,6 @@ function _test_27632(A)
end
# check that this doesn't crash
_test_27632(view(ones(Int64, (1, 1, 1)), 1, 1, 1))

# issue #29608 - views of single values can be considered contiguous
@test Base.iscontiguous(view(ones(1), 1))