目的

与 抽象工厂 类似，静态工厂模式用于创建一系列互相关联或依赖的对象。它与抽象工厂模式的区别在于，静态工厂模式仅使用 一个静态方法 来创建所有它可以创建的类型。通常，这个静态方法被命名为：factory 或 build。

UML 图

1.8.3. 代码

StaticFactory.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Creational\StaticFactory;

use InvalidArgumentException;

/**
 * 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
{
    public static function factory(string $type): Formatter
    {
        if ($type == 'number') {
            return new FormatNumber();
        } elseif ($type == 'string') {
            return new FormatString();
        }

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

Formatter.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Creational\StaticFactory;

interface Formatter
{
    public function format(string $input): string;
}

FormatString.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Creational\StaticFactory;

class FormatString implements Formatter
{
    public function format(string $input): string
    {
        return $input;
    }
}

FormatNumber.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Creational\StaticFactory;

class FormatNumber implements Formatter
{
    public function format(string $input): string
    {
        return number_format((int) $input);
    }
}

测试

Tests/StaticFactoryTest.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Creational\StaticFactory\Tests;

use InvalidArgumentException;
use DesignPatterns\Creational\StaticFactory\FormatNumber;
use DesignPatterns\Creational\StaticFactory\FormatString;
use DesignPatterns\Creational\StaticFactory\StaticFactory;
use PHPUnit\Framework\TestCase;

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

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

    public function testException()
    {
        $this->expectException(InvalidArgumentException::class);

        StaticFactory::factory('object');
    }
}