mow.cli enum custom type

enum.go

package enum

import (
	"fmt"
	"strings"

	"github.com/pkg/errors"
)

type Value struct {
	Value string
	Desc  string
}

func New(values ...Value) *Enum {
	return &Enum{
		Values: values,
	}
}

type Enum struct {
	Values []Value
	Value  string
}

func (e *Enum) Set(v string) error {
	for _, s := range e.Values {
		if v == s.Value {
			e.Value = v
			return nil
		}
	}

	possible := make([]string, len(e.Values))
	for i, v := range e.Values {
		possible[i] = fmt.Sprintf("%q", v.Value)
	}

	return errors.Errorf("invalid value %q. Must be one of: %s", v, strings.Join(possible, ", "))
}

func (e *Enum) Desc(desc string) string {
	var res strings.Builder
	res.WriteString(desc)
	res.WriteString("\n")

	for i, v := range e.Values {
		if i > 0 {
			res.WriteString("\n")
		}
		res.WriteString(" - ")
		res.WriteString(v.Value)
		res.WriteString(": ")
		res.WriteString(v.Desc)
	}

	return res.String()
}

func (e *Enum) String() string {
	return e.Value
}

main.go

package main

import (
	"fmt"
	"os"

	cli "github.com/jawher/mow.cli"
)

func main() {
	app := cli.App("enum", "enum usage example")

	mode := enum.New(
		enum.Value{
			Value: "read", Desc: "read mode",
		},
		enum.Value{
			Value: "write", Desc: "write mode",
		})
	app.VarOpt("m", mode, mode.Desc("file open mode"))

	force := app.BoolOpt("f force", false, "force open")

	app.Action = func() {
		fmt.Printf("mode:  %v\n", mode.Value)
		fmt.Printf("force: %v\n", *force)

	}
	app.Run(os.Args)
}