str_conc_test.go

/*
 go test str_conc_test.go -bench . -benchtime 10s
BenchmarkConcatOne-4     	 2000000	      7684 ns/op
BenchmarkConcatTwo-4     	 5000000	      2883 ns/op
BenchmarkConcatThree-4   	 5000000	      2933 ns/op
PASS
ok  	command-line-arguments	56.982s
*/

package main

import (
	"bytes"
	"strconv"
	"testing"
)

var ids = []int{30028, 300300, 200200, 123928, 89282, 832892, 238983, 30028, 300300, 200200, 123928, 89282, 832892, 238983, 30028, 300300, 200200, 123928, 89282, 832892, 238983, 30028, 300300, 200200, 123928, 89282, 832892, 238983}

func BenchmarkConcatOne(b *testing.B) {
	for i := 0; i < b.N; i++ {
		concatOne(ids)
	}
}

func BenchmarkConcatTwo(b *testing.B) {
	for i := 0; i < b.N; i++ {
		concatTwo(ids)
	}
}

func BenchmarkConcatThree(b *testing.B) {
	for i := 0; i < b.N; i++ {
		concatThree(ids)
	}
}

func concatOne(ids []int) string {
	res := ""
	for _, id := range ids {
		if len(res) > 0 {
			res += ","
		}
		res += strconv.Itoa(id)
	}
	return res
}

const averageIdLen = 6

func concatTwo(ids []int) string {
	buf := bytes.NewBuffer(make([]byte, 0, (averageIdLen+1)*len(ids)))
	for _, id := range ids {
		if buf.Len() > 0 {
			buf.WriteString(",")
		}
		buf.WriteString(strconv.Itoa(id))
	}
	return buf.String()
}

func concatThree(ids []int) string {
	buf := bytes.NewBuffer(make([]byte, 0, (averageIdLen+1)*len(ids)))
	comma := ","
	for _, id := range ids {
		if buf.Len() > 0 {
			buf.WriteString(comma)
		}
		buf.WriteString(strconv.Itoa(id))
	}
	return buf.String()
}