golang slow range array

main_test.go

package main

import (
	"testing"
)

var MyArray = [100]int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99}
var MyVar int

func BenchmarkArray(b *testing.B) {
	for i := 0; i < b.N; i++ {
		for _, n := range MyArray {
			MyVar = n
		}
	}
}

func BenchmarkSlice(b *testing.B) {
	for i := 0; i < b.N; i++ {
		for _, n := range MyArray[:] {
			MyVar = n
		}
	}
}

func BenchmarkArrayPointer(b *testing.B) {
	for i := 0; i < b.N; i++ {
		for _, n := range &MyArray {
			MyVar = n
		}
	}
}

func BenchmarkArrayIndex(b *testing.B) {
	for i := 0; i < b.N; i++ {
		for j := 0; j < len(MyArray); j++ {
			v := MyArray[j]
			MyVar = v
		}
	}
}

output

# go test -v -bench=. ./
testing: warning: no tests to run
PASS
BenchmarkArray-8       	10000000	       119 ns/op
BenchmarkSlice-8       	20000000	        65.2 ns/op
BenchmarkArrayPointer-8	20000000	        79.9 ns/op
BenchmarkArrayIndex-8  	20000000	        94.8 ns/op
ok  	tmp/v6j	6.370s