php 模仿静态

class StringUtil {
    private static $instance;

    private function __construct() {}

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

    public static function toUpperCase($str) {
        return strtoupper($str);
    }

    public static function toLowerCase($str) {
        return strtolower($str);
    }
}

// 使用静态方法
echo StringUtil::toUpperCase("Hello, World!"); // 输出: HELLO, WORLD!
echo StringUtil::toLowerCase("Hello, World!"); // 输出: hello, world!

// 使用单例模式
$util = StringUtil::getInstance();
echo $util->toUpperCase("Hello, World!"); // 输出: HELLO, WORLD!

class Example {
    private $value;

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

    public static function printValue(Example $instance) {
        echo $instance->value;
    }
}

$instance = new Example("Hello");
Example::printValue($instance); // 输出: Hello

class Counter {
    private static $count = 0;
    private static $lock;

    public static function increment() {
        if (self::$lock === null) {
            self::$lock = new SplLock();
        }
        self::$lock->lock();
        self::$count++;
        self::$lock->unlock();
    }

    public static function getCount() {
        return self::$count;
    }
}

Counter::increment();
Counter::increment();
echo Counter::getCount(); // 输出: 2