2.2. Bridge

2.2.1. Purpose

Decouple an abstraction from its implementation so that the two can varyindependently.

2.2.2. Examples

• SymfonyDoctrineBridge

2.2.3. UML Diagram

2.2.4. Code

You can also find this code on GitHub

FormatterInterface.php

<?php
 
namespace DesignPatterns\Structural\Bridge;
 
interface FormatterInterface
{
    public function format(string $text);
}

PlainTextFormatter.php

<?php
 
namespace DesignPatterns\Structural\Bridge;
 
class PlainTextFormatter implements FormatterInterface
{
    public function format(string $text)
    {
        return $text;
    }
}

HtmlFormatter.php

<?php
 
namespace DesignPatterns\Structural\Bridge;
 
class HtmlFormatter implements FormatterInterface
{
    public function format(string $text)
    {
        return sprintf('<p>%s</p>', $text);
    }
}

Service.php

<?php
 
namespace DesignPatterns\Structural\Bridge;
 
abstract class Service
{
    /**
     * @var FormatterInterface
     */
    protected $implementation;
 
    /**
     * @param FormatterInterface $printer
     */
    public function __construct(FormatterInterface $printer)
    {
        $this->implementation = $printer;
    }
 
    /**
     * @param FormatterInterface $printer
     */
    public function setImplementation(FormatterInterface $printer)
    {
        $this->implementation = $printer;
    }
 
    abstract public function get();
}

HelloWorldService.php

<?php
 
namespace DesignPatterns\Structural\Bridge;
 
class HelloWorldService extends Service
{
    public function get()
    {
        return $this->implementation->format('Hello World');
    }
}

2.2.5. Test

Tests/BridgeTest.php

<?php
 
namespace DesignPatterns\Structural\Bridge\Tests;
 
use DesignPatterns\Structural\Bridge\HelloWorldService;
use DesignPatterns\Structural\Bridge\HtmlFormatter;
use DesignPatterns\Structural\Bridge\PlainTextFormatter;
use PHPUnit\Framework\TestCase;
 
class BridgeTest extends TestCase
{
    public function testCanPrintUsingThePlainTextPrinter()
    {
        $service = new HelloWorldService(new PlainTextFormatter());
        $this->assertEquals('Hello World', $service->get());
 
        // now change the implementation and use the HtmlFormatter instead
        $service->setImplementation(new HtmlFormatter());
        $this->assertEquals('<p>Hello World</p>', $service->get());
    }
}