go map iteration uses memory allocation when we need a pointer of key/value, even within empty maps!

func BenchmarkMap(b *testing.B) {
    var m map[byte]struct{}
    var p *byte
    for i := 0; i < b.N; i++ {
        for k := range m {
            p = &k
            _ = p
        }
    }
}

$ go test -bench=Map -benchmem
BenchmarkMap-4 51860970 23.70 ns/op 1 B/op 1 allocs/op

$ #expected result:
BenchmarkMap-4 51860970 23.70 ns/op 0 B/op 0 allocs/op