Go Methods and Inheritance

main.go

package main

import (
	"fmt"
)

// We create a normat struct that represent normal inovice
type Invoice struct {
	Id     string
	Amount int
	isPaid bool
}

// Here is a method to alter the value of isPaid
// altering value require `*` sign before struct signature
// if there is no `*` then it wont be altered
func (i *Invoice) AlterToPaid() {
	i.isPaid = true
}

// If the value does not alter, it is better to use
// non asterisk.
func (i Invoice) PrintStatus() {
	fmt.Println(i.Id, "is paid? ", i.isPaid)
}

// Make another struct that requires an
// Invoice struct address
type Payment struct {
	Invoice *Invoice
}

// Another example where it requires an
// actual Invoice
type PaymentLater struct {
	Invoice Invoice
}

// Add method that return number
func (pl PaymentLater) GetSomeNumber() int {
	return int(3)
}

// struct Payemnt engine inherit the Invoice component
// and all its method. there is an example later
type PaymentEngine struct {
	PaymentLater
}

// Overriding the previous method
func (pe PaymentEngine) GetSomeNumber() int {
	return pe.PaymentLater.GetSomeNumber() + 3
}

func main() {
  // both that invoice and invoice address should be able to 
  // access its own method
  
  // example for actual invoice
	i1 := Invoice{Id: "I1"}
	i1.PrintStatus()
	i1.AlterToPaid()
	i1.Id = "I1 Alter"
	i1.PrintStatus()
  
  // example for address invoice
	i2 := &Invoice{Id: "I2"}
	i2.PrintStatus()
	i2.AlterToPaid()
	i2.Id = "I2 Alter"
	i2.PrintStatus()
	
  // both invoice should have its `isPaid` to be true
	fmt.Println(i1, i2)
	
  // Payment only accept invoice address not actual invoice
	p1 := Payment{i2}
	p1.Invoice.Id = "I2 Alter Payment" // will alter invoice id
	fmt.Println(i1, i2)
	
  // PaymentLater accept actual invoice 
	p2 := PaymentLater{i1}
	p2.Invoice.Id = "I1 Alter Payment" // will not alter invoice id
	fmt.Println(i1, i2)
	
  // Method overriding
	fmt.Println(p2.GetSomeNumber()) // should return 3
	pe := PaymentEngine{} // Not declaring PaymentLater as a input but still have its method
	someNumber := pe.GetSomeNumber() // should return 3 + 3 = 6
	fmt.Println(someNumber)
}