[GO] Append vs Copy

alloc_bench_test.go

package main

import (
	"fmt"
	"runtime"
	"testing"
)

func BenchmarkAppend(b *testing.B) {
	for i := 0; i < b.N; i++ {
		i1 := []int{1, 2, 3}
		i2 := []int{4, 5, 6}
		o := make([]int, 0, len(i1)+len(i2))
		o = append(o, i1...)
		o = append(o, i2...)
	}
	b.ReportAllocs()
}

func BenchmarkCopy(b *testing.B) {
	for i := 0; i < b.N; i++ {
		i1 := []int{1, 2, 3}
		i2 := []int{4, 5, 6}
		o := make([]int, len(i1)+len(i2))
		copy(o, i1)
		copy(o[:len(i1)], i2)
	}
	b.ReportAllocs()
}

func main() {
	bench("copy", BenchmarkCopy)
	bench("append", BenchmarkAppend)
}

func bench(label string, fn func(b *testing.B)) {
	fmt.Printf("=== Running %q ===\n", label)

	var (
		startAllocs runtime.MemStats
		endAllocs   runtime.MemStats
	)

	runtime.ReadMemStats(&startAllocs)
	res := testing.Benchmark(fn)
	fmt.Println(res)

	runtime.ReadMemStats(&endAllocs)
	fmt.Printf("> Allocs: %d\n", endAllocs.Mallocs-startAllocs.Mallocs)
}