2.1. Adapter / Wrapper

2.1.1. Purpose

To translate one interface for a class into a compatible interface. Anadapter allows classes to work together that normally could not becauseof incompatible interfaces by providing its interface to clients whileusing the original interface.

2.1.2. Examples

• DB Client libraries adapter
• using multiple different webservices and adapters normalize data sothat the outcome is the same for all

2.1.3. UML Diagram

2.1.4. Code

You can also find this code on GitHub

BookInterface.php

<?php
 
namespace DesignPatterns\Structural\Adapter;
 
interface BookInterface
{
    public function turnPage();
 
    public function open();
 
    public function getPage(): int;
}

Book.php

<?php
 
namespace DesignPatterns\Structural\Adapter;
 
class Book implements BookInterface
{
    /**
     * @var int
     */
    private $page;
 
    public function open()
    {
        $this->page = 1;
    }
 
    public function turnPage()
    {
        $this->page++;
    }
 
    public function getPage(): int
    {
        return $this->page;
    }
}

EBookAdapter.php

<?php
 
namespace DesignPatterns\Structural\Adapter;
 
/**
 * This is the adapter here. Notice it implements BookInterface,
 * therefore you don't have to change the code of the client which is using a Book
 */
class EBookAdapter implements BookInterface
{
    /**
     * @var EBookInterface
     */
    protected $eBook;
 
    /**
     * @param EBookInterface $eBook
     */
    public function __construct(EBookInterface $eBook)
    {
        $this->eBook = $eBook;
    }
 
    /**
     * This class makes the proper translation from one interface to another.
     */
    public function open()
    {
        $this->eBook->unlock();
    }
 
    public function turnPage()
    {
        $this->eBook->pressNext();
    }
 
    /**
     * notice the adapted behavior here: EBookInterface::getPage() will return two integers, but BookInterface
     * supports only a current page getter, so we adapt the behavior here
     *
     * @return int
     */
    public function getPage(): int
    {
        return $this->eBook->getPage()[0];
    }
}

EBookInterface.php

<?php
 
namespace DesignPatterns\Structural\Adapter;
 
interface EBookInterface
{
    public function unlock();
 
    public function pressNext();
 
    /**
     * returns current page and total number of pages, like [10, 100] is page 10 of 100
     *
     * @return int[]
     */
    public function getPage(): array;
}

Kindle.php

<?php
 
namespace DesignPatterns\Structural\Adapter;
 
/**
 * this is the adapted class. In production code, this could be a class from another package, some vendor code.
 * Notice that it uses another naming scheme and the implementation does something similar but in another way
 */
class Kindle implements EBookInterface
{
    /**
     * @var int
     */
    private $page = 1;
 
    /**
     * @var int
     */
    private $totalPages = 100;
 
    public function pressNext()
    {
        $this->page++;
    }
 
    public function unlock()
    {
    }
 
    /**
     * returns current page and total number of pages, like [10, 100] is page 10 of 100
     *
     * @return int[]
     */
    public function getPage(): array
    {
        return [$this->page, $this->totalPages];
    }
}

2.1.5. Test

Tests/AdapterTest.php

<?php
 
namespace DesignPatterns\Structural\Adapter\Tests;
 
use DesignPatterns\Structural\Adapter\Book;
use DesignPatterns\Structural\Adapter\EBookAdapter;
use DesignPatterns\Structural\Adapter\Kindle;
use PHPUnit\Framework\TestCase;
 
class AdapterTest extends TestCase
{
    public function testCanTurnPageOnBook()
    {
        $book = new Book();
        $book->open();
        $book->turnPage();
 
        $this->assertEquals(2, $book->getPage());
    }
 
    public function testCanTurnPageOnKindleLikeInANormalBook()
    {
        $kindle = new Kindle();
        $book = new EBookAdapter($kindle);
 
        $book->open();
        $book->turnPage();
 
        $this->assertEquals(2, $book->getPage());
    }
}