1. Error

package main

import "fmt"

type Error struct {
	errCode uint8
}

func (e *Error) Error() string {
	switch e.errCode {
	case 1:
		return "file not found"
	case 2:
		return "time out"
	default:
		return "unknown error"
	}
}

func main() {
	err := new(Error)
	err.errCode = 2
	msg := err.Error()
	fmt.Println(msg)
}