join.go

package lib

var s string

//go:noinline
func Join(a []string, sep string) string {
	n := len(sep) * (len(a) - 1)
	for i := 0; i < len(a); i++ {
		n += len(a[i])
	}

	zzzzzzzzzzzzzzzzzzzzzzzzzzz := make([]byte, n)
	bp := copy(zzzzzzzzzzzzzzzzzzzzzzzzzzz, a[0])
	for _, s := range a[1:] {
		bp += copy(zzzzzzzzzzzzzzzzzzzzzzzzzzz[bp:], sep)
		bp += copy(zzzzzzzzzzzzzzzzzzzzzzzzzzz[bp:], s)
	}
	return string(zzzzzzzzzzzzzzzzzzzzzzzzzzz)
}

//go:noinline
func hi() string {
	tojoin := []string{
		"a string to join with others",
		"a second string",
	}
	return Join(tojoin, ",")
}

join_test.go

package lib

import (
	"strings"
	"testing"
)

var sink string

func BenchmarkJoinOne(b *testing.B) {
	tojoin := []string{"a string to join with others"}
	for i := 0; i < b.N; i++ {
		sink = strings.Join(tojoin, ",")
	}
}

func BenchmarkJoinTwo(b *testing.B) {
	tojoin := []string{"a string to join with others", "a second string"}
	for i := 0; i < b.N; i++ {
		sink = strings.Join(tojoin, ",")
	}
}

func BenchmarkJoinThree(b *testing.B) {
	tojoin := []string{"a string to join with others", "a second string", "a third string"}
	for i := 0; i < b.N; i++ {
		sink = strings.Join(tojoin, ",")
	}
}

func BenchmarkJoinMany(b *testing.B) {
	tojoin := []string{
		"a string to join with others",
		"a second string",
		"a third string",
		"a fourth string that is quite a bit longer than the others",
		"a fifth string",
		"6",
		"number seven",
		"8",
		"nine",
		"the final string which is number ten",
	}
	for i := 0; i < b.N; i++ {
		sink = strings.Join(tojoin, ",")
	}
}