String append vs string builder vs bytes buffer

main_test.go

package main

import (
	"bytes"
	"strings"
	"testing"
)

func BenchmarkStringAppend(b *testing.B) {
	for i := 0; i < b.N; i++ {
		f()
	}
}

func BenchmarkStringBuilder(b *testing.B) {
	for i := 0; i < b.N; i++ {
		g()
	}
}

func BenchmarkBytesBuffer(b *testing.B) {
	for i := 0; i < b.N; i++ {
		h()
	}
}
func h() string {
	var s bytes.Buffer
	s.WriteString("foo")
	s.WriteString("bar")
	s.WriteString("car")
	return s.String()
}

func f() string {
	var s string
	s += "foo"
	s += "bar"
	s += "car"
	return s
}

func g() string {
	var sb strings.Builder
	sb.WriteString("foo")
	sb.WriteString("bar")
	sb.WriteString("car")
	return sb.String()
}

output

goos: darwin
goarch: amd64
pkg: scratch
cpu: Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
BenchmarkStringAppend-16        10825950                96.49 ns/op
BenchmarkStringBuilder-16       20359875                65.87 ns/op
BenchmarkBytesBuffer-16         13561768                82.57 ns/op
PASS
ok      scratch 4.470s