Broadcasting *= and the like

General Usage
2

Broadcasting *= doesn’t seem to be a problem, but you’re allocating a temporary array at each iteration i when saying radicals[i:i:end]. You can avoid this by either using @views or the loop you’ve commented out.

julia> using BenchmarkTools

julia> function getradicals1(limit)
           radicals = ones(Int64, limit)

           for i ∈ Iterators.filter(x -> isone(radicals[x]), 2:length(radicals))
               radicals[i:i:end] .*= i
               #for j ∈ i:i:length(radicals)
               #    radicals[j] *= i
               #end
           end

           radicals
       end
getradicals1 (generic function with 1 method)

julia> @btime getradicals1(100);
  1.560 μs (26 allocations: 4.33 KiB)

julia> function getradicals2(limit)
           radicals = ones(Int64, limit)

           for i ∈ Iterators.filter(x -> isone(radicals[x]), 2:length(radicals))
               @views radicals[i:i:end] .*= i
               #for j ∈ i:i:length(radicals)
               #    radicals[j] *= i
               #end
           end

           radicals
       end
getradicals2 (generic function with 1 method)

julia> @btime getradicals2(100);
  824.390 ns (1 allocation: 896 bytes)

julia> function getradicals3(limit)
           radicals = ones(Int64, limit)

           for i ∈ Iterators.filter(x -> isone(radicals[x]), 2:length(radicals))
               #radicals[i:i:end] .*= i
               for j ∈ i:i:length(radicals)
                   radicals[j] *= i
               end
           end

           radicals
       end
getradicals3 (generic function with 1 method)

julia> @btime getradicals3(100);
  414.065 ns (1 allocation: 896 bytes)
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