const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"

func randomString(n int) string {
	b := make([]byte, n)
	for i := range b {
		b[i] = letterBytes[rand.Intn(len(letterBytes))]
	}
	return string(b)
}

func plusConcat(n int, str string) string {
	s := ""
	for i := 0; i < n; i++ {
		s += str
	}
	return s
}

func sprintfConcat(n int, str string) string {
	s := ""
	for i := 0; i < n; i++ {
		s = fmt.Sprintf("%s%s", s, str)
	}
	return s
}

func builderConcat(n int, str string) string {
	var builder strings.Builder
	for i := 0; i < n; i++ {
		builder.WriteString(str)
	}
	return builder.String()
}

func bufferConcat(n int, s string) string {
	buf := new(bytes.Buffer)
	for i := 0; i < n; i++ {
		buf.WriteString(s)
	}
	return buf.String()
}

func byteConcat(n int, str string) string {
	buf := make([]byte, 0)
	for i := 0; i < n; i++ {
		buf = append(buf, str...)
	}
	return string(buf)
}

func preByteConcat(n int, str string) string {
	buf := make([]byte, 0, n*len(str))
	for i := 0; i < n; i++ {
		buf = append(buf, str...)
	}
	return string(buf)
}

func benchmark(b *testing.B, f func(int, string) string) {
	var str = randomString(10)
	for i := 0; i < b.N; i++ {
		f(10000, str)
	}
}

func BenchmarkPlusConcat(b *testing.B)    { benchmark(b, plusConcat) }
func BenchmarkSprintfConcat(b *testing.B) { benchmark(b, sprintfConcat) }
func BenchmarkBuilderConcat(b *testing.B) { benchmark(b, builderConcat) }
func BenchmarkBufferConcat(b *testing.B)  { benchmark(b, bufferConcat) }
func BenchmarkByteConcat(b *testing.B)    { benchmark(b, byteConcat) }
func BenchmarkPreByteConcat(b *testing.B) { benchmark(b, preByteConcat) }

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go test  -bench=. -benchmem .
goos: darwin
goarch: arm64
pkg: main/demo
cpu: Apple M4 Pro
BenchmarkPlusConcat-12                36          32238928 ns/op        530999857 B/op     10045 allocs/op
BenchmarkSprintfConcat-12             20          56848854 ns/op        833393446 B/op     34184 allocs/op
BenchmarkBuilderConcat-12          23143             51218 ns/op          514804 B/op         23 allocs/op
BenchmarkBufferConcat-12           29152             40997 ns/op          368578 B/op         13 allocs/op
BenchmarkByteConcat-12             19549             60984 ns/op          621301 B/op         24 allocs/op
BenchmarkPreByteConcat-12          50913             24879 ns/op          212994 B/op          2 allocs/op
PASS
ok      main/demo       10.263s

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