Play with interfaces and zero-value objects

gistfile1.txt

package main

import (
	"errors"
	"fmt"
)

type MyError string

func (e MyError) Error() string {
	return string(e)
}

const Err1 = MyError("Err1")

func genErr(f bool) error {
	var e error
	if f {
		e = Err1
	}
	return e
}

func genErrSpecificType(f bool) error {
	var e MyError
	if f {
		e = Err1
	}
	return e
}

func playWithNilErrors() {
	// true
	fmt.Println(genErr(false) == nil)
	// false
	fmt.Println(genErr(true) == nil)


	// false <- error is an interface. Its nil value has no such type. But the variable inside
	// `genErrSpecificType` is declared as MyError, which has a type. So it is not nil.
	fmt.Println(genErrSpecificType(false) == nil)
	// false
	fmt.Println(genErrSpecificType(true) == nil)
}

func main() {
	playWithNilErrors()
}