Avoid string-to-byte conversion

Do not create byte slices from a fixed string repeatedly. Instead, perform theconversion once and capture the result.

BadGood
  1. for i := 0; i < b.N; i++ {
  2.   w.Write([]byte("Hello world"))
  3. }
 
  1. data := []byte("Hello world")
  2. for i := 0; i < b.N; i++ {
  3.   w.Write(data)
  4. }
  1. BenchmarkBad-4   50000000   22.2 ns/op
 
  1. BenchmarkGood-4  500000000   3.25 ns/op