Encapsulation with an interface

interface.go

package account

import (
	"errors"
)

type CheckingAccount struct {
	balance int
}

func (a *CheckingAccount) Pay(amount int) error {
	if a.balance-amount < 0 {
		return errors.New("not enough funds")
	}
	a.balance = a.balance - amount
	return nil
}

func (a *CheckingAccount) Deposit(amount int) {
	a.balance = a.balance + amount
}

func (a *CheckingAccount) Balance() int {
	return a.balance
}

func CreateAccount() *CheckingAccount {
	return &CheckingAccount{}
}
// -----------------
package main

import (
	"fmt"
	
	"account"
)

type Account interface {
	Pay(amount int) error
	Deposit(amount int)
	Balance() int
}

func main() {

	var acc Account
	acc = account.CreateAccount()
	acc.Deposit(18)
	fmt.Printf("balance is: %d\n", acc.Balance())

	acc.Pay(10)
	fmt.Printf("balance is: %d\n", acc.Balance())
}