1package main
 2
 3import (
 4	"errors"
 5	"fmt"
 6)
 7
 8type Bitcoin int
 9
10func (b Bitcoin) String() string {
11	return fmt.Sprintf("%d BTC", b)
12}
13
14type Wallet struct {
15	balance Bitcoin
16}
17
18var InsufficientFundsError = errors.New("cannot withdraw, insufficient funds")
19
20func (w *Wallet) Deposit(amount Bitcoin) {
21	fmt.Printf("address of balance in test is %v \n", &w.balance)
22	w.balance += amount
23}
24
25func (w *Wallet) Balance() Bitcoin {
26	fmt.Printf("address of balance in test is %v \n", &w.balance)
27	return w.balance
28}
29
30func (w *Wallet) Withdraw(amount Bitcoin) error {
31	if amount > w.balance {
32		return InsufficientFundsError
33	}
34
35	w.balance -= amount
36	return nil
37}