go2go: Optional

main.go

package main

import (
	"fmt"
	"github.com/moaible/goptional" // yet not repository
)

func main() {
	var baseValue = 1
	var var1 *int = nil
	var var2 *int = &baseValue
	op1 := goptional.New(var1)
	op2 := goptional.New(var2)
	var t, f bool = true, false
	var ret *bool
	op1.If(func(v *int) {
		fmt.Println("1: Presented", *v)
	}).OrElse(func() {
		ret = &f
		fmt.Println("1: Not Presented")
	})
	fmt.Println(*ret)
	fmt.Println(*op1.ValueOr(var2))
	op2.If(func(v *int) {
		ret = &t
		fmt.Println("2: Presented", *v)
	})
	fmt.Println(*ret)
}

optional.go

package optional

import (
	"reflect"
)

type Optional(type T interface{}) struct {
	value interface{}
}

type OptionalEmpty(type T interface{}) struct {}

func New(type T interface{})(value T) *Optional(T) {
	return &Optional(T){
		value: &value,
	}
}

func (o *Optional(T)) Value() T {
	return *o.value.(*T)
}

func (o *Optional(T)) Has() bool {
	// FIXME: don't want to use refrect if possible
	return !reflect.ValueOf(*o.value.(*T)).IsNil()
}

func (o *Optional(T)) ValueOr(option T) T {
	if o.Has() {
		return *o.value.(*T)
	} else {
		return option
	}
}

func (o *Optional(T)) If(presenting func(T)) *OptionalEmpty(T) {
	if o.Has() {
		presenting(o.Value())
		return nil
	}
	return &OptionalEmpty(T){}
}

func (o *OptionalEmpty(T)) OrElse(presenting func()) {
	presenting()
}

Click here for a working demo
https://go2goplay.golang.org/p/6CUvn2aXJuU