1.9. Static Factory

1.9.1. Purpose

Similar to the AbstractFactory, this pattern is used to create series of related or dependent objects. The difference between this and the abstract factory pattern is that the static factory pattern uses just one static method to create all types of objects it can create. It is usually named factory or build.

1.9.2. Examples

  • Zend Framework: Zend_Cache_Backend or _Frontend use a factory method create cache backends or frontends

1.9.3. UML Diagram

Alt StaticFactory UML Diagram

1.9.4. Code

You can also find these code on GitHub

StaticFactory.php

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<?php

namespace DesignPatterns\Creational\StaticFactory;

/**
 * Note1: Remember, static means global state which is evil because it can't be mocked for tests
 * Note2: Cannot be subclassed or mock-upped or have multiple different instances.
 */
final class StaticFactory
{
    /**
     * @param string $type
     *
     * @return FormatterInterface
     */
    public static function factory(string $type): FormatterInterface
    {
        if ($type == 'number') {
            return new FormatNumber();
        }

        if ($type == 'string') {
            return new FormatString();
        }

        throw new \InvalidArgumentException('Unknown format given');
    }
}

FormatterInterface.php

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<?php

namespace DesignPatterns\Creational\StaticFactory;

interface FormatterInterface
{
}

FormatString.php

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<?php

namespace DesignPatterns\Creational\StaticFactory;

class FormatString implements FormatterInterface
{
}

FormatNumber.php

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<?php

namespace DesignPatterns\Creational\StaticFactory;

class FormatNumber implements FormatterInterface
{
}

1.9.5. Test

Tests/StaticFactoryTest.php

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<?php

namespace DesignPatterns\Creational\StaticFactory\Tests;

use DesignPatterns\Creational\StaticFactory\StaticFactory;
use PHPUnit\Framework\TestCase;

class StaticFactoryTest extends TestCase
{
    public function testCanCreateNumberFormatter()
    {
        $this->assertInstanceOf(
            'DesignPatterns\Creational\StaticFactory\FormatNumber',
            StaticFactory::factory('number')
        );
    }

    public function testCanCreateStringFormatter()
    {
        $this->assertInstanceOf(
            'DesignPatterns\Creational\StaticFactory\FormatString',
            StaticFactory::factory('string')
        );
    }

    /**
     * @expectedException \InvalidArgumentException
     */
    public function testException()
    {
        StaticFactory::factory('object');
    }
}