3.10. State

3.10.1. Purpose

Encapsulate varying behavior for the same routine based on an object’s state. This can be a cleaner way for an object to change its behavior at runtime without resorting to large monolithic conditional statements.

3.10.2. UML Diagram

Alt State UML Diagram

3.10.3. Code

You can also find this code on GitHub

OrderContext.php

 1<?php
 2
 3declare(strict_types=1);
 4
 5namespace DesignPatterns\Behavioral\State;
 6
 7class OrderContext
 8{
 9    private State $state;
10
11    public static function create(): OrderContext
12    {
13        $order = new self();
14        $order->state = new StateCreated();
15
16        return $order;
17    }
18
19    public function setState(State $state)
20    {
21        $this->state = $state;
22    }
23
24    public function proceedToNext()
25    {
26        $this->state->proceedToNext($this);
27    }
28
29    public function toString()
30    {
31        return $this->state->toString();
32    }
33}

State.php

 1<?php
 2
 3declare(strict_types=1);
 4
 5namespace DesignPatterns\Behavioral\State;
 6
 7interface State
 8{
 9    public function proceedToNext(OrderContext $context);
10
11    public function toString(): string;
12}

StateCreated.php

 1<?php
 2
 3declare(strict_types=1);
 4
 5namespace DesignPatterns\Behavioral\State;
 6
 7class StateCreated implements State
 8{
 9    public function proceedToNext(OrderContext $context)
10    {
11        $context->setState(new StateShipped());
12    }
13
14    public function toString(): string
15    {
16        return 'created';
17    }
18}

StateShipped.php

 1<?php
 2
 3declare(strict_types=1);
 4
 5namespace DesignPatterns\Behavioral\State;
 6
 7class StateShipped implements State
 8{
 9    public function proceedToNext(OrderContext $context)
10    {
11        $context->setState(new StateDone());
12    }
13
14    public function toString(): string
15    {
16        return 'shipped';
17    }
18}

StateDone.php

 1<?php
 2
 3declare(strict_types=1);
 4
 5namespace DesignPatterns\Behavioral\State;
 6
 7class StateDone implements State
 8{
 9    public function proceedToNext(OrderContext $context)
10    {
11        // there is nothing more to do
12    }
13
14    public function toString(): string
15    {
16        return 'done';
17    }
18}

3.10.4. Test

Tests/StateTest.php

 1<?php
 2
 3declare(strict_types=1);
 4
 5namespace DesignPatterns\Behavioral\State\Tests;
 6
 7use DesignPatterns\Behavioral\State\OrderContext;
 8use PHPUnit\Framework\TestCase;
 9
10class StateTest extends TestCase
11{
12    public function testIsCreatedWithStateCreated()
13    {
14        $orderContext = OrderContext::create();
15
16        $this->assertSame('created', $orderContext->toString());
17    }
18
19    public function testCanProceedToStateShipped()
20    {
21        $contextOrder = OrderContext::create();
22        $contextOrder->proceedToNext();
23
24        $this->assertSame('shipped', $contextOrder->toString());
25    }
26
27    public function testCanProceedToStateDone()
28    {
29        $contextOrder = OrderContext::create();
30        $contextOrder->proceedToNext();
31        $contextOrder->proceedToNext();
32
33        $this->assertSame('done', $contextOrder->toString());
34    }
35
36    public function testStateDoneIsTheLastPossibleState()
37    {
38        $contextOrder = OrderContext::create();
39        $contextOrder->proceedToNext();
40        $contextOrder->proceedToNext();
41        $contextOrder->proceedToNext();
42
43        $this->assertSame('done', $contextOrder->toString());
44    }
45}