julia> using FastBroadcast
julia> function fast_foo9(a, b, c, d, e, f, g, h, i)
           @.. a = b + 0.1 * (0.2c + 0.3d + 0.4e + 0.5f + 0.6g + 0.6h + 0.6i)
           nothing
       end
fast_foo9 (generic function with 1 method)
julia> function foo9(a, b, c, d, e, f, g, h, i)
           @. a = b + 0.1 * (0.2c + 0.3d + 0.4e + 0.5f + 0.6g + 0.6h + 0.6i)
           nothing
       end
foo9 (generic function with 1 method)
julia> a, b, c, d, e, f, g, h, i = [rand(100, 100, 2) for i in 1:9];
julia> using BenchmarkTools
julia> @btime fast_foo9($a, $b, $c, $d, $e, $f, $g, $h, $i);
  19.902 μs (0 allocations: 0 bytes)
julia> @btime foo9($a, $b, $c, $d, $e, $f, $g, $h, $i);
  81.457 μs (0 allocations: 0 bytes)

julia> b = [1.0];
julia> @btime foo9($a, $b, $c, $d, $e, $f, $g, $h, $i);
  70.634 μs (0 allocations: 0 bytes)
julia> @btime fast_foo9($a, $b, $c, $d, $e, $f, $g, $h, $i);
  131.470 μs (0 allocations: 0 bytes)

julia> using FastBroadcast
julia> function foo_serial!(dest, src)
           @.. thread=false dest = log(src)
       end
foo_serial! (generic function with 1 method)
julia> function foo_parallel!(dest, src)
           @.. thread=true dest = log(src)
       end
foo_parallel! (generic function with 1 method)
julia> function foo_maybe_parallel!(dest, src, thread)
           @.. thread=thread dest = log(src)
       end
foo_maybe_parallel! (generic function with 1 method)
julia> src = rand(10^4); dest = similar(src);
julia> @btime foo_serial!($dest, $src);
  50.860 μs (0 allocations: 0 bytes)
julia> @btime foo_parallel!($dest, $src);
  17.245 μs (1 allocation: 48 bytes)
julia> @btime foo_maybe_parallel!($dest, $src, $FastBroadcast.False());
  51.682 μs (0 allocations: 0 bytes)
julia> @btime foo_maybe_parallel!($dest, $src, $FastBroadcast.True());
  17.360 μs (1 allocation: 48 bytes)