Enum types (bitshifted too)

enum.go

package main

import (
  "fmt"
  "strings"
)

type foo int
const (
  One foo = iota
  Two
  Three
  Four
)

var fooNames = [...]string{
  One:   "One",
  Two:   "Two",
  Three: "Three",
  Four:  "Four",
}

func (f foo) String() string {
  return fooNames[f]
}

type mask int
const (
  Read mask = 1 << iota
  Write
  Async
)

var maskNames = [...]string{
  Read:  "Read",
  Write: "Write",
  Async: "Async",
}

func (m mask) String() string {
  var masks []string
  for i := Read; i <= Async; i <<= 1 {
    if m & i != 0 {
      masks = append(masks, maskNames[i])
    }
  }
  return strings.Join(masks, " | ")
}

func main() {
  for _, val := range []foo{One,Two,Three,Four} {
    fmt.Printf("(%T) %v %v\n", val, int(val), val)
  }
  for _, val := range []mask{
  	Read,
  	Write,
  	Async,
  	Read | Async,
  	Write | Async,
  	Read | Write,
  	Read | Write | Async,
  } {
  	fmt.Printf("(%T) %v %v\n", val, int(val), val)
  }
}

xxOutput

(main.foo) 0 One
(main.foo) 1 Two
(main.foo) 2 Three
(main.foo) 3 Four
(main.mask) 1 Read
(main.mask) 2 Write
(main.mask) 4 Async
(main.mask) 5 Read | Async
(main.mask) 6 Write | Async
(main.mask) 3 Read | Write
(main.mask) 7 Read | Write | Async