How do I use isassigned with a Matrix?

New to Julia
3

It looks like this is a bug julia#47942 in the isassigned code. What it does is to convert 500, 514 to a (zero-based) linear index and check that this is < length(a), which succeeds here because 500-1 + (514-1) * size(a, 1) < length(a).

This check ensures that the linear index is in-bounds (so it prevents jl_array_isassigned from crashing) but it is not a sufficient check of the multidimensional indices.

Maybe @tim.holy can comment further, because the code originated in julia#11167 way back in 2015 (for Julia 0.4).

That being said, if you just want a bounds check (which is all isassigned can do for Matrix{Float64}), you can call checkindex or checkbounds:

julia> checkindex(Bool, axes(a,1), 500) && checkindex(Bool, axes(a,2), 514)
false

julia> checkbounds(a, 500, 514)
ERROR: BoundsError: attempt to access 161×517 Matrix{Float64} at index [500, 514]
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