handle_specific_error.go

package main

import (
	"errors"
	"fmt"
	"reflect"
)

var SimpleValidationError = errors.New("Validation error")

type ValidationError struct {
	Field   string
	Message string
}

func (e ValidationError) Error() string {
	return e.Field + " " + e.Message
}

func main() {
	var err error

	// 0. Compare error message
	err = func() error {
		return errors.New("Some error")
	}()

	if err != nil {
		if err.Error() == "Some error" {
			fmt.Println(err.Error())
		}
	}

	// 1. Compare global error object
	err = func() error {
		return SimpleValidationError
	}()

	if err != nil {
		if err == SimpleValidationError {
			fmt.Println(err.Error())
		}
	

	// 2. Compare type of error object
	err = func() error {
		return ValidationError{Field: "name", Message: "is too long"}
	}()

	if err != nil {
		if reflect.TypeOf(err) == reflect.TypeOf(ValidationError{}) {
			fmt.Println(err.Error())
		}
	}
}