for_key_issues1.go

package main

import "fmt"

type S struct {
	b [8]byte
}

func main() {
	mmap := map[S]struct{}{
		S{b: [8]byte{1}}: struct{}{},
		S{b: [8]byte{2}}: struct{}{},
	}

	var z [][]byte

	for k := range mmap {
		z = append(z, k.b[:])
	}

	fmt.Println(z)
}