check if a view is contiguous in julia

Question

I have a N-dim julia array and a view of a slice. Is there a way to check if this view is contiguous (that would be a.flags["F"] in NumPy)? It seems Base.iscontiguous is not the answer.

a = ones((1,1,1))
t = (1:1, 1:1, 1:1)
v = @view a[t...]
println(Base.iscontiguous(v))  # false
Base.iscontiguous(a[t...])  # MethodError: no method matching iscontiguous(::Array{Float64, 3}) 

Here I know the underlying data block is contiguous, but is there a way to check it for more complex views?

Answer 1

iscontiguous implementation:

    iscontiguous(A::SubArray) = iscontiguous(typeof(A))
    iscontiguous(::Type{<:SubArray}) = false
    iscontiguous(::Type{<:FastContiguousSubArray}) = true

Your view is not a FastContiguousSubArray:

    julia> typeof(v)
    SubArray{Float64, 3, Array{Float64, 3}, Tuple{UnitRange{Int64}, UnitRange{Int64}, UnitRange{Int64}}, false}

where

    help?> SubArray
    search: SubArray BitArray Array DenseArray StridedArray
    
      SubArray{T,N,P,I,L} <: AbstractArray{T,N}
    
      N-dimensional view into a parent array (of type P) with an element type T, restricted by a tuple of indices (of type
      I). L is true for types that support fast linear indexing, and false otherwise. [...]

which you can also verify by:

    julia> Base.viewindexing(v.indices)
    IndexCartesian()

Take a look at the Linear indexing section in the manual.