Go Example

package main

import "fmt"

type hasItemState struct {
    vendingMachine *vendingMachine
}

func (i *hasItemState) requestItem() error {
    if i.vendingMachine.itemCount == 0 {
        i.vendingMachine.setState(i.vendingMachine.noItem)
        return fmt.Errorf("No item present")
    }
    fmt.Printf("Item requestd\n")
    i.vendingMachine.setState(i.vendingMachine.itemRequested)
    return nil
}

func (i *hasItemState) addItem(count int) error {
    fmt.Printf("%d items added\n", count)
    i.vendingMachine.incrementItemCount(count)
    return nil
}

func (i *hasItemState) insertMoney(money int) error {
    return fmt.Errorf("Please select item first")
}
func (i *hasItemState) dispenseItem() error {
    return fmt.Errorf("Please select item first")
}

package main

import "fmt"

type hasMoneyState struct {
    vendingMachine *vendingMachine
}

func (i *hasMoneyState) requestItem() error {
    return fmt.Errorf("Item dispense in progress")
}

func (i *hasMoneyState) addItem(count int) error {
    return fmt.Errorf("Item dispense in progress")
}

func (i *hasMoneyState) insertMoney(money int) error {
    return fmt.Errorf("Item out of stock")
}
func (i *hasMoneyState) dispenseItem() error {
    fmt.Println("Dispensing Item")
    i.vendingMachine.itemCount = i.vendingMachine.itemCount - 1
    if i.vendingMachine.itemCount == 0 {
        i.vendingMachine.setState(i.vendingMachine.noItem)
    } else {
        i.vendingMachine.setState(i.vendingMachine.hasItem)
    }
    return nil
}

package main

import "fmt"

type itemRequestedState struct {
    vendingMachine *vendingMachine
}

func (i *itemRequestedState) requestItem() error {
    return fmt.Errorf("Item already requested")
}

func (i *itemRequestedState) addItem(count int) error {
    return fmt.Errorf("Item Dispense in progress")
}

func (i *itemRequestedState) insertMoney(money int) error {
    if money < i.vendingMachine.itemPrice {
        fmt.Errorf("Inserted money is less. Please insert %d", i.vendingMachine.itemPrice)
    }
    fmt.Println("Money entered is ok")
    i.vendingMachine.setState(i.vendingMachine.hasMoney)
    return nil
}
func (i *itemRequestedState) dispenseItem() error {
    return fmt.Errorf("Please insert money first")
}

package main

import "fmt"

type noItemState struct {
    vendingMachine *vendingMachine
}

func (i *noItemState) requestItem() error {
    return fmt.Errorf("Item out of stock")
}

func (i *noItemState) addItem(count int) error {
    i.vendingMachine.incrementItemCount(count)
    i.vendingMachine.setState(i.vendingMachine.hasItem)
    return nil
}

func (i *noItemState) insertMoney(money int) error {
    return fmt.Errorf("Item out of stock")
}
func (i *noItemState) dispenseItem() error {
    return fmt.Errorf("Item out of stock")
}

package main

type state interface {
    addItem(int) error
    requestItem() error
    insertMoney(money int) error
    dispenseItem() error
}

package main

import "fmt"

type vendingMachine struct {
    hasItem       state
    itemRequested state
    hasMoney      state
    noItem        state

    currentState state

    itemCount int
    itemPrice int
}

func newVendingMachine(itemCount, itemPrice int) *vendingMachine {
    v := &vendingMachine{
        itemCount: itemCount,
        itemPrice: itemPrice,
    }
    hasItemState := &hasItemState{
        vendingMachine: v,
    }
    itemRequestedState := &itemRequestedState{
        vendingMachine: v,
    }
    hasMoneyState := &hasMoneyState{
        vendingMachine: v,
    }
    noItemState := &noItemState{
        vendingMachine: v,
    }

    v.setState(hasItemState)
    v.hasItem = hasItemState
    v.itemRequested = itemRequestedState
    v.hasMoney = hasMoneyState
    v.noItem = noItemState
    return v
}

func (v *vendingMachine) requestItem() error {
    return v.currentState.requestItem()
}

func (v *vendingMachine) addItem(count int) error {
    return v.currentState.addItem(count)
}

func (v *vendingMachine) insertMoney(money int) error {
    return v.currentState.insertMoney(money)
}

func (v *vendingMachine) dispenseItem() error {
    return v.currentState.dispenseItem()
}

func (v *vendingMachine) setState(s state) {
    v.currentState = s
}

func (v *vendingMachine) incrementItemCount(count int) {
    fmt.Printf("Adding %d items\n", count)
    v.itemCount = v.itemCount + count
}

package main

import (
    "fmt"
    "log"
)

func main() {
    vendingMachine := newVendingMachine(1, 10)

    err := vendingMachine.requestItem()
    if err != nil {
        log.Fatalf(err.Error())
    }

    err = vendingMachine.insertMoney(10)
    if err != nil {
        log.Fatalf(err.Error())
    }

    err = vendingMachine.dispenseItem()
    if err != nil {
        log.Fatalf(err.Error())
    }

    fmt.Println()

    err = vendingMachine.addItem(2)
    if err != nil {
        log.Fatalf(err.Error())
    }

    fmt.Println()

    err = vendingMachine.requestItem()
    if err != nil {
        log.Fatalf(err.Error())
    }

    err = vendingMachine.insertMoney(10)
    if err != nil {
        log.Fatalf(err.Error())
    }

    err = vendingMachine.dispenseItem()
    if err != nil {
        log.Fatalf(err.Error())
    }
}

Item requestd
Money entered is ok
Dispensing Item

Adding 2 items

Item requestd
Money entered is ok
Dispensing Item