permission_set.go

// https://go.dev/play/p/1nLXyCDe1_3
// because UNIX! 🐣
package main

import "fmt"

var (
	Read    = Permission{0x1}
	Write   = Permission{0x2}
	Execute = Permission{0x4}
)

type Permission struct{ v uint8 }

var ss = map[Permission]string{
	Permission{}:                 "---",
	Read:                         "r--",
	Write:                        "-w-",
	Execute:                      "--e",
	Read.Add(Write):              "rw-",
	Read.Add(Execute):            "r-e",
	Write.Add(Execute):           "-we",
	Read.Add(Write).Add(Execute): "rwe",
}

func (a Permission) String() string { return ss[a] }

func (a Permission) Add(b Permission) Permission { return Permission{a.v | b.v} }

func (a Permission) Contains(b Permission) bool { return b.v&(a.v&b.v) == b.v }

func main() {
	fmt.Println(Read)
	fmt.Println(Read.Contains(Read.Add(Write)))
	fmt.Println(Read.Add(Write).Contains(Read))
	fmt.Println(Read.Add(Write).Contains(Execute))
	fmt.Println(Read.Add(Write).Add(Execute))
}