PHP中的设计模式：如何实现单例和工厂模式

<?php

class Singleton {
    private static $instance;

    private function __construct() {
        // 私有构造函数，防止外部实例化
    }

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

    public function doSomething() {
        echo "Singleton is doing something!\n";
    }
}

// 获取单例实例
$instance1 = Singleton::getInstance();
$instance2 = Singleton::getInstance();

// 验证是否为同一个实例
if ($instance1 === $instance2) {
    echo "Singleton works!\n";
}

$instance1->doSomething();
?>

<?php

interface Product {
    public function operation();
}

class ConcreteProductA implements Product {
    public function operation() {
        return "Product A\n";
    }
}

class ConcreteProductB implements Product {
    public function operation() {
        return "Product B\n";
    }
}

class Factory {
    public static function createProduct($type) {
        switch ($type) {
            case 'A':
                return new ConcreteProductA();
            case 'B':
                return new ConcreteProductB();
            default:
                throw new InvalidArgumentException("Invalid product type: " . $type);
        }
    }
}

// 使用工厂创建对象
try {
    $productA = Factory::createProduct('A');
    echo $productA->operation();

    $productB = Factory::createProduct('B');
    echo $productB->operation();

    // 尝试创建未知的对象类型
    $productC = Factory::createProduct('C'); // 这将抛出异常
    echo $productC->operation();

} catch (InvalidArgumentException $e) {
    echo "Error: " . $e->getMessage() . "\n";
}

?>

<?php

trait SingletonTrait {
    private static $instance;

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

    private function __construct() {} // 防止外部实例化
    private function __clone() {}     // 防止克隆
    private function __wakeup() {}    // 防止反序列化
}

class MyClass {
    use SingletonTrait;

    public function doSomething() {
        echo "MyClass is doing something!\n";
    }
}

$instance1 = MyClass::getInstance();
$instance2 = MyClass::getInstance();

if ($instance1 === $instance2) {
    echo "MyClass Singleton works!\n";
}

$instance1->doSomething();

?>

<?php

require 'vendor/autoload.php';

use DI\ContainerBuilder;

interface Logger {
    public function log(string $message);
}

class FileLogger implements Logger {
    private $file;

    public function __construct(string $file) {
        $this->file = $file;
    }

    public function log(string $message) {
        file_put_contents($this->file, $message . "\n", FILE_APPEND);
    }
}

class MyService {
    private $logger;

    public function __construct(Logger $logger) {
        $this->logger = $logger;
    }

    public function doSomething(string $message) {
        $this->logger->log($message);
        echo "Service did something: " . $message . "\n";
    }
}


$containerBuilder = new ContainerBuilder();
$containerBuilder->addDefinitions([
    Logger::class => DI\create(FileLogger::class)->constructor('log.txt'),
]);
$container = $containerBuilder->build();

$myService = $container->get(MyService::class);
$myService->doSomething("Hello, world!");

?>