go_enum_iota.go

package main

import (
	"fmt"
	"math"
	"strconv"
)

// I used bitwise operations on iota.
// This will be handy when we want to represent months together.
// Like: April | May

type Month uint32

const (
	January  Month = 1 << iota // iota automatically increases by 1 on each line
	February                   // 1 << 2
	March                      // 1 << 3
	April                      // 1 << 4
	May                        // 1 << 5
	June                       // ...
	July
	August
	September
	November
	December

	AllMonths = January | February | March | April | May | June | July | August |
		September | November | December
)

// String returns the name of a month
//
// This attaches a method String to Month constant
//
// Tip: You can use Stringer to create string representation of enums automatically
//      https://godoc.org/golang.org/x/tools/cmd/stringer
func (m Month) String() string {
	names := []string{"January", "February", "March", "April", "May", "June",
		"July", "August", "September", "November", "December"}

	// if it's power of 2, then it's a singular Month value
	if m&(m-1) == 0 {
		// returns the index of the bit to select the month name from `names`
		// array
		return names[int(math.Log2(float64(m)))]
	} else {
		// for composites, just return its number
		// exercise for you: return the names of the months in a composite Month
		return strconv.Itoa(int(m))
	}
}

func main() {
	// for each month
	for i := 1; i < 12; i++ {
		month := Month((1 << uint(i-1)))

		// name of the month: April.String()
		// value of the month: April
		//
		// Printf automatically calls .String() method when it sees a %s
		// Printf automatically converts to a numeric when it sees a %d
		fmt.Printf("%s: %d\n", month, month)
	}

	// AllMonths contains all of the months
	fmt.Println("All Months:", AllMonths)
}