Exhibit of the advantage of copy vs append

benchmp.md

$ benchcmp old.txt new.txt 
benchmark          old ns/op     new ns/op     delta
BenchmarkBy*-4     319           99.4          -68.84%
BenchmarkBy*-4     318           138           -56.60%
BenchmarkBy*-4     321           88.7          -72.37%
BenchmarkBy*-4     320           90.2          -71.81%
BenchmarkBy*-4     319           85.9          -73.07%

benchmark          old allocs     new allocs     delta
BenchmarkBy*-4     4              1              -75.00%
BenchmarkBy*-4     4              1              -75.00%
BenchmarkBy*-4     4              1              -75.00%
BenchmarkBy*-4     4              1              -75.00%
BenchmarkBy*-4     4              1              -75.00%

benchmark          old bytes     new bytes     delta
BenchmarkBy*-4     240           80            -66.67%
BenchmarkBy*-4     240           80            -66.67%
BenchmarkBy*-4     240           80            -66.67%
BenchmarkBy*-4     240           80            -66.67%
BenchmarkBy*-4     240           80            -66.67%

copy-vs-append-exhibit_test.go

package main

import (
	"fmt"
	"testing"
)

var sample = []interface{}{"a", 1, 20.9, fmt.Println, 'Z'}

func byCopy(il []interface{}) []interface{} {
	icl := make([]interface{}, len(il))
	copy(icl, il)
	return icl
}

func byAppend(il []interface{}) []interface{} {
	var icl []interface{}
	for _, iv := range il {
		icl = append(icl, iv)
	}
	return icl
}

func BenchmarkByAppend(b *testing.B) {
	for i := 0; i < b.N; i++ {
		if tl := byAppend(sample); tl != nil {
		}
	}
	b.ReportAllocs()
}

func BenchmarkByCopy(b *testing.B) {
	for i := 0; i < b.N; i++ {
		if tl := byCopy(sample); tl != nil {
		}
	}
	b.ReportAllocs()
}

new.txt

BenchmarkBy*-4     	20000000	        99.4 ns/op	      80 B/op	       1 allocs/op
BenchmarkBy*-4     	10000000	       138 ns/op	      80 B/op	       1 allocs/op
BenchmarkBy*-4     	20000000	        88.7 ns/op	      80 B/op	       1 allocs/op
BenchmarkBy*-4     	20000000	        90.2 ns/op	      80 B/op	       1 allocs/op
BenchmarkBy*-4     	20000000	        85.9 ns/op	      80 B/op	       1 allocs/op

old.txt

BenchmarkBy*-4   	 5000000	       319 ns/op	     240 B/op	       4 allocs/op
BenchmarkBy*-4   	 5000000	       318 ns/op	     240 B/op	       4 allocs/op
BenchmarkBy*-4   	 5000000	       321 ns/op	     240 B/op	       4 allocs/op
BenchmarkBy*-4   	 5000000	       320 ns/op	     240 B/op	       4 allocs/op
BenchmarkBy*-4   	 5000000	       319 ns/op	     240 B/op	       4 allocs/op