GoLang benchmark for aggregating of multiple slice elements into a single slice

benchmark_slice_aggregation.go

package test
//
//  Initial source for benchmark from https://stackoverflow.com/a/40678026/102699
//  Added BenchmarkConcatAppendPreAllocate()
//
import "testing"

func BenchmarkConcatCopyPreAllocate(b *testing.B) {
	for n := 0; n < b.N; n++ {
		B = concatCopyPreAllocate(slices)
	}
}

func BenchmarkConcatAppendPreAllocate(b *testing.B) {
	for n := 0; n < b.N; n++ {
		B = concatAppendPreAllocate(slices)
	}
}

func BenchmarkConcatAppend(b *testing.B) {
	for n := 0; n < b.N; n++ {
		B = concatAppend(slices)
	}
}

var slices = [][]byte{
	[]byte("my first slice"),
	[]byte("second slice"),
	[]byte("third slice"),
	[]byte("fourth slice"),
	[]byte("fifth slice"),
}

var B []byte

func concatAppendPreAllocate(slices [][]byte) []byte {
	var totalLen int
	for _, s := range slices {
		totalLen += len(s)
	}
	tmp := make([]byte, 0, totalLen)
	for _, s := range slices {
		tmp = append(tmp,s...)
	}
	return tmp
}

func concatCopyPreAllocate(slices [][]byte) []byte {
	var totalLen int
	for _, s := range slices {
		totalLen += len(s)
	}
	tmp := make([]byte, totalLen)
	var i int
	for _, s := range slices {
		i += copy(tmp[i:], s)
	}
	return tmp
}

func concatAppend(slices [][]byte) []byte {
	var tmp []byte
	for _, s := range slices {
		tmp = append(tmp, s...)
	}
	return tmp
}

results.txt

goos: darwin
goarch: amd64
cpu: Intel(R) Core(TM) i7-4870HQ CPU @ 2.50GHz
BenchmarkConcatCopyPreAllocate
BenchmarkConcatCopyPreAllocate-8     	19351508	        62.89 ns/op
BenchmarkConcatAppendPreAllocate
BenchmarkConcatAppendPreAllocate-8   	20998980	        57.53 ns/op
BenchmarkConcatAppend
BenchmarkConcatAppend-8              	 8931429	       132.0 ns/op
PASS