compare two style of copy golang slice performance

golangcopylistbench.go

package gotrial

import (
	"strings"
	"testing"
)

func copyListV1(in []string) []string {
	var out []string

	for _, s := range in {
		out = append(out, s)
	}

	return out
}

func copyListV2(in []string) []string {
	out := make([]string, len(in))

	for i, s := range in {
		out[i] = s
	}

	return out
}

var input = strings.Fields(`Making code faster is exciting, and benchmarks in Go make that easy to do! Not really. 
Optimizing a program can be complex and require careful consideration to do properly. 
Daniel demonstrates techniques and tools which are a must for any performance aficionado.`)

func BenchmarkCopyList(b *testing.B) {
	b.ReportAllocs()

	for i := 0; i < b.N; i++ {
		copyListV2(input)
	}
}

➜  gotrial go get golang.org/x/perf/cmd/benchstat
➜  gotrial benchstat v1.txt v2.txt
name         old time/op    new time/op    delta
CopyList-12     703ns ± 0%     190ns ± 0%   ~     (p=1.000 n=1+1)

name         old alloc/op   new alloc/op   delta
CopyList-12    2.03kB ± 0%    0.70kB ± 0%   ~     (p=1.000 n=1+1)

name         old allocs/op  new allocs/op  delta
CopyList-12      7.00 ± 0%      1.00 ± 0%   ~     (p=1.000 n=1+1)