nil_check_working.go

nil_check_working.go

package main

import (
	"fmt"
	"reflect"
)

type Animal interface {
	MakeSound() string
}

type Dog struct{}

func (d *Dog) MakeSound() string {
	return "Bark"
}

type Cat struct{}

func (c Cat) MakeSound() string {
	return "Meow"
}

func isNil(i interface{}) bool {
	return i == nil || reflect.ValueOf(i).IsNil()
}

func isNilFixed(i interface{}) bool {
	if i == nil {
		return true
	}
	switch reflect.TypeOf(i).Kind() {
	case reflect.Ptr, reflect.Map, reflect.Array, reflect.Chan, reflect.Slice:
		return reflect.ValueOf(i).IsNil()
	}
	return false
}

func isNilBetter(i Animal) bool {
	var ret bool
	switch i.(type) {
	case *Dog:
		v := i.(*Dog)
		ret = v == nil
	case Cat:
		ret = false
	}

	return ret
}

func main() {
	var d *Dog = nil
	var a Animal = d

	fmt.Println(isNilFixed(a))

	var c Cat
	a = c
	fmt.Println(isNilFixed(a))

	var m map[string] string
	fmt.Println(isNilFixed(m))

	var s []string
	fmt.Println(isNilFixed(s))

	var ch chan string
	fmt.Println(isNilFixed(ch))
}

Thank you very much for your gist and for your post

Here below you can find my two cents

func myIsNil(i Animal) bool {
	var ret bool
	switch i.(type) {
	case *Dog:
		v := i.(*Dog)
		ret = v == nil
	case Cat:
		ret = false
        default:
                 ret = isNilFixed(i)  // so isNilFixed() is called only if we forgot to implement some cases
                 // add some log to remember to add new cases to the switch to improve performance
	}
	return ret
}

Ciao,
Antonio

Thanks for the gist, but I found something weird in it and double-checked in the playground and the code isNilFixed would actually panic in the Array case, because arrays can not be nil. Can you confirm?