抽象工厂-经典设计模式PHP版

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抽象工厂模式

是一种创建型设计模式，它能创建一系列相关的对象，而无需指定其具体类。

假设你正在开发一款家具商店模拟器。你的代码中包括一些类，用于表示：

一系列相关产品，例如椅子 Chair 、沙发 Sofa 和咖啡桌 CoffeeTable 。
系列产品的不同变体。例如，你可以使用现代 Modern 、维多利亚 Victorian 、装饰风艺术 ArtDeco 等风格生成椅子、沙发和咖啡桌。

你需要设法单独生成每件家具对象，这样才能确保其风格一致。如果顾客收到的家具风格不一样，他们可不会开心。

此外，你也不希望在添加新产品或新风格时修改已有代码。家具供应商对于产品目录的更新非常频繁，你不会想在每次更新时都去修改核心代码的。

解决方案

首先，抽象工厂模式建议为系列中的每件产品明确声明接口（例如椅子、沙发或咖啡桌）。然后，确保所有产品变体都继承这些接口。例如，所有风格的椅子都实现椅子接口；所有风格的咖啡桌都实现咖啡桌接口，以此类推。

接下来，我们需要声明抽象工厂——包含系列中所有产品构造方法的接口。例如 createChair 创建椅子、 createSofa 创建沙发和 createCoffeeTable 创建咖啡桌。这些方法必须返回抽象产品类型，即我们之前抽取的那些接口：椅子，沙发和咖啡桌等等。

那么该如何处理产品变体呢？对于系列产品的每个变体，我们都将基于抽象工厂接口创建不同的工厂类。每个工厂类都只能返回特定类别的产品，例如，现代家具工厂 ModernFurnitureFactory 只能创建现代椅子 ModernChair 、现代沙发 ModernSofa 和现代咖啡桌 ModernCoffeeTable 对象。

客户端代码可以通过相应的抽象接口调用工厂和产品类。你无需修改实际客户端代码，就能更改传递给客户端的工厂类，也能更改客户端代码接收的产品变体。

假设客户端想要工厂创建一把椅子。客户端无需了解工厂类，也不用管工厂类创建出的椅子类型。无论是现代风格，还是维多利亚风格的椅子，对于客户端来说没有分别，它只需调用抽象椅子接口就可以了。这样一来，客户端只需知道椅子以某种方式实现了 sitOn 坐下方法就足够了。此外，无论工厂返回的是何种椅子变体，它都会和由同一工厂对象创建的沙发或咖啡桌风格一致。

最后一点说明：如果客户端仅接触抽象接口，那么谁来创建实际的工厂对象呢？一般情况下，应用程序会在初始化阶段创建具体工厂对象。而在此之前，应用程序必须根据配置文件或环境设定选择工厂类别。

抽象产品（Abstract Product）为构成系列产品的一组不同但相关的产品声明接口。
具体产品（Concrete Product）是抽象产品的多种不同类型实现。所有变体（维多利亚/现代）都必须实现相应的抽象产品（椅子/沙发）。
抽象工厂（Abstract Factory）接口声明了一组创建各种抽象产品的方法。
具体工厂（Concrete Factory）实现抽象工厂的构建方法。每个具体工厂都对应特定产品变体，且仅创建此种产品变体。
尽管具体工厂会对具体产品进行初始化，其构建方法签名必须返回相应的抽象产品。这样，使用工厂类的客户端代码就不会与工厂创建的特定产品变体耦合。客户端（Client）只需通过抽象接口调用工厂和产品对象，就能与任何具体工厂/ 产品变体交互。

代码示例

<?php
/**
 * Abstract Factory Design Pattern
 *
 * Intent: Lets you produce families of related objects without specifying their
 * concrete classes.
 *
 * Example: In this example, the Abstract Factory pattern provides an
 * infrastructure for creating various types of templates for different elements
 * of a web page.
 *
 * A web application can support different rendering engines at the same time,
 * but only if its classes are independent of the concrete classes of rendering
 * engines. Hence, the application's objects must communicate with template
 * objects only via their abstract interfaces. Your code should not create the
 * template objects directly, but delegate their creation to special factory
 * objects. Finally, your code should not depend on the factory objects either
 * but, instead, should work with them via the abstract factory interface.
 *
 * As a result, you will be able to provide the app with the factory object that
 * corresponds to one of the rendering engines. All templates, created in the
 * app, will be created by that factory and their type will match the type of
 * the factory. If you decide to change the rendering engine, you'll be able to
 * pass a new factory to the client code, without breaking any existing code.
 */
/**
 * The Abstract Factory interface declares creation methods for each distinct
 * product type.
 */
interface TemplateFactory
{
    public function createTitleTemplate(): TitleTemplate;
    public function createPageTemplate(): PageTemplate;
    public function getRenderer(): TemplateRenderer;
}
/**
 * Each Concrete Factory corresponds to a specific variant (or family) of
 * products.
 *
 * This Concrete Factory creates Twig templates.
 */
class TwigTemplateFactory implements TemplateFactory
{
    public function createTitleTemplate(): TitleTemplate
    {
        return new TwigTitleTemplate();
    }
    public function createPageTemplate(): PageTemplate
    {
        return new TwigPageTemplate($this->createTitleTemplate());
    }
    public function getRenderer(): TemplateRenderer
    {
        return new TwigRenderer();
    }
}
/**
 * And this Concrete Factory creates PHPTemplate templates.
 */
class PHPTemplateFactory implements TemplateFactory
{
    public function createTitleTemplate(): TitleTemplate
    {
        return new PHPTemplateTitleTemplate();
    }
    public function createPageTemplate(): PageTemplate
    {
        return new PHPTemplatePageTemplate($this->createTitleTemplate());
    }
    public function getRenderer(): TemplateRenderer
    {
        return new PHPTemplateRenderer();
    }
}
/**
 * Each distinct product type should have a separate interface. All variants of
 * the product must follow the same interface.
 *
 * For instance, this Abstract Product interface describes the behavior of page
 * title templates.
 */
interface TitleTemplate
{
    public function getTemplateString(): string;
}
/**
 * This Concrete Product provides Twig page title templates.
 */
class TwigTitleTemplate implements TitleTemplate
{
    public function getTemplateString(): string
    {
        return "<h1>{{ title }}</h1>";
    }
}
/**
 * And this Concrete Product provides PHPTemplate page title templates.
 */
class PHPTemplateTitleTemplate implements TitleTemplate
{
    public function getTemplateString(): string
    {
        return "<h1><?= \$title; ?></h1>";
    }
}
/**
 * This is another Abstract Product type, which describes whole page templates.
 */
interface PageTemplate
{
    public function getTemplateString(): string;
}
/**
 * The page template uses the title sub-template, so we have to provide the way
 * to set it in the sub-template object. The abstract factory will link the page
 * template with a title template of the same variant.
 */
abstract class BasePageTemplate implements PageTemplate
{
    protected $titleTemplate;
    public function __construct(TitleTemplate $titleTemplate)
    {
        $this->titleTemplate = $titleTemplate;
    }
}
/**
 * The Twig variant of the whole page templates.
 */
class TwigPageTemplate extends BasePageTemplate
{
    public function getTemplateString(): string
    {
        $renderedTitle = $this->titleTemplate->getTemplateString();
        return <<<HTML
        <div class="page">
            $renderedTitle
            <article class="content">{{ content }}</article>
        </div>
        HTML;
    }
}
/**
 * The PHPTemplate variant of the whole page templates.
 */
class PHPTemplatePageTemplate extends BasePageTemplate
{
    public function getTemplateString(): string
    {
        $renderedTitle = $this->titleTemplate->getTemplateString();
        return <<<HTML
        <div class="page">
            $renderedTitle
            <article class="content"><?= \$content; ?></article>
        </div>
        HTML;
    }
}
/**
 * The renderer is responsible for converting a template string into the actual
 * HTML code. Each renderer behaves differently and expects its own type of
 * template strings passed to it. Baking templates with the factory let you pass
 * proper types of templates to proper renders.
 */
interface TemplateRenderer
{
    public function render(string $templateString, array $arguments = []): string;
}
/**
 * The renderer for Twig templates.
 */
class TwigRenderer implements TemplateRenderer
{
    public function render(string $templateString, array $arguments = []): string
    {
        return \Twig::render($templateString, $arguments);
    }
}
/**
 * The renderer for PHPTemplate templates. Note that this implementation is very
 * basic, if not crude. Using the `eval` function has many security
 * implications, so use it with caution in real projects.
 */
class PHPTemplateRenderer implements TemplateRenderer
{
    public function render(string $templateString, array $arguments = []): string
    {
        extract($arguments);
        ob_start();
        eval(' ?>' . $templateString . '<?php ');
        $result = ob_get_contents();
        ob_end_clean();
        return $result;
    }
}
/**
 * The client code. Note that it accepts the Abstract Factory class as the
 * parameter, which allows the client to work with any concrete factory type.
 */
class Page
{
    public $title;
    public $content;
    public function __construct($title, $content)
    {
        $this->title = $title;
        $this->content = $content;
    }
    // Here's how would you use the template further in real life. Note that the
    // page class does not depend on any concrete template classes.
    public function render(TemplateFactory $factory): string
    {
        $pageTemplate = $factory->createPageTemplate();
        $renderer = $factory->getRenderer();
        return $renderer->render($pageTemplate->getTemplateString(), [
            'title' => $this->title,
            'content' => $this->content
        ]);
    }
}
/**
 * Now, in other parts of the app, the client code can accept factory objects of
 * any type.
 */
$page = new Page('Sample page', 'This it the body.');
echo "Testing actual rendering with the PHPTemplate factory:\n";
echo $page->render(new PHPTemplateFactory());
// Uncomment the following if you have Twig installed.
// echo "Testing rendering with the Twig factory:\n"; echo $page->render(new
// TwigTemplateFactory());