PHP 函数设计模式应用基础

class Singleton {
  private static $instance;

  public static function getInstance() {
    if (!isset(self::$instance)) {
      self::$instance = new Singleton();
    }

    return self::$instance;
  }

  private function __construct() {
    // 构造代码
  }
}

class Database {
  private static $connection;

  public static function getConnection() {
    if (!isset(self::$connection)) {
      self::$connection = new PDO('...');
    }

    return self::$connection;
  }
}

interface Shape {
  public function draw();
}

class Square implements Shape {
  public function draw() {
    // 绘制正方形
  }
}

class Circle implements Shape {
  public function draw() {
    // 绘制圆形
  }
}

class ShapeFactory {
  public static function createShape($type) {
    switch ($type) {
      case 'circle':
        return new Circle();

      case 'square':
        return new Square();

      default:
        throw new Exception('Invalid shape type');
    }
  }
}

class FormElement {
  // 通用属性和方法
}

class Input extends FormElement {
  public function render() {
    // 输入元素 HTML 代码
  }
}

class Textarea extends FormElement {
  public function render() {
    // 文本区域元素 HTML 代码
  }
}

class FormElementFactory {
  public static function createElement($type) {
    switch ($type) {
      case 'input':
        return new Input();

      case 'textarea':
        return new Textarea();

      default:
        throw new Exception('Invalid element type');
    }
  }
}