2.1. Adapter / Wrapper

2.1.1. Purpose

To translate one interface for a class into a compatible interface. An adapter allows classes to work together that normally could not because of incompatible interfaces by providing its interface to clients while using the original interface.

2.1.2. Examples

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

2.1.3. UML Diagram

Alt Adapter UML Diagram

2.1.4. Code

You can also find this code on GitHub

Book.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Structural\Adapter;

interface Book
{
    public function turnPage();

    public function open();

    public function getPage(): int;
}

PaperBook.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Structural\Adapter;

class PaperBook implements Book
{
    private int $page;

    public function open()
    {
        $this->page = 1;
    }

    public function turnPage()
    {
        $this->page++;
    }

    public function getPage(): int
    {
        return $this->page;
    }
}

EBook.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Structural\Adapter;

interface EBook
{
    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;
}

EBookAdapter.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Structural\Adapter;

/**
 * This is the adapter here. Notice it implements Book,
 * therefore you don't have to change the code of the client which is using a Book
 */
class EBookAdapter implements Book
{
    public function __construct(protected 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: EBook::getPage() will return two integers, but Book
     * supports only a current page getter, so we adapt the behavior here
     */
    public function getPage(): int
    {
        return $this->eBook->getPage()[0];
    }
}

Kindle.php

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<?php declare(strict_types=1);

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 EBook
{
    private int $page = 1;
    private int $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

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<?php declare(strict_types=1);

namespace DesignPatterns\Structural\Adapter\Tests;

use DesignPatterns\Structural\Adapter\PaperBook;
use DesignPatterns\Structural\Adapter\EBookAdapter;
use DesignPatterns\Structural\Adapter\Kindle;
use PHPUnit\Framework\TestCase;

class AdapterTest extends TestCase
{
    public function testCanTurnPageOnBook()
    {
        $book = new PaperBook();
        $book->open();
        $book->turnPage();

        $this->assertSame(2, $book->getPage());
    }

    public function testCanTurnPageOnKindleLikeInANormalBook()
    {
        $kindle = new Kindle();
        $book = new EBookAdapter($kindle);

        $book->open();
        $book->turnPage();

        $this->assertSame(2, $book->getPage());
    }
}