julia> A = zero(SMatrix{2,2,Float64})
julia> @set A[CartesianIndex(1,1)] = 4
ERROR: MethodError: no method matching setindex(::SMatrix{2, 2, Float64, 4}, ::Int64, ::CartesianIndex{2})
Closest candidates are:
  setindex(::CartesianIndex, ::Any, ::Any) at multidimensional.jl:100
  setindex(::StaticArray, ::Any, ::Int64) at ~/.julia/packages/StaticArrays/58yy1/src/deque.jl:185
  setindex(::StaticArray, ::Any, ::Int64...) at ~/.julia/packages/StaticArrays/58yy1/src/deque.jl:198