Performance issues with CartesianIndices

General Usage Performance
3

It’s often wise to explicitly specialize on any inner-loop function passed as an argument, and this resolves issue 3:

function splatting_fnfill_nd!(A::AbstractArray{<:Any,K}, f::F, D::Int) where {K, F}
    for I ∈ CartesianIndices(ntuple(_ -> D, Val(K)))
        A[I] = f(Tuple(I)...)
    end
    return A
end

julia> let buf = MMatrix{3,3,Bool}(undef)
           result = @btime splatting_fnfill_nd!($buf, kron2, 3)
           @assert result == I[1:3, 1:3]
           println()
           @code_warntype splatting_fnfill_nd!(buf, kron2, 3)
       end;
  4.900 ns (0 allocations: 0 bytes)
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