php-object-oriented (5)

1. Review: In the previous article, we learned about abstract classes, interfaces and characteristics

2. In this article, we will learn about overloading!

3. Overloading: Use magic method to achieve

3.1 Summary

      （1）php中的重载是指动态的创建类属性和方法
      （2）当调用当前环境下未定义或不可见的类属性或方法时，重载方法会被调用
      （3）所有的重载方法都必须声明为 public
      （4）通过魔术方法的参数都不能通过引用传递
      （5）和传统的面向对象重载不同
      （6）传统的重载是用于提供多个同名类方法，各方法参数类型和个数不同
      （7）isset() 和 unset()  魔术方法
      （8）callStatic() php5.3

  3.2属性重载

   演示一个例子：

<pre name="code">       # __set __get __isset ,__unset
     class MemberTest {
      /**  被重载的数据保存在此  */
    private $data = array();

 
    /**  重载不能被用在已经定义的属性  */
    public $declared = 1;

       /**  只有从类外部访问这个属性时，重载才会发生 */
    private $hidden = 2;

    public function __set($name, $value) {
        echo "Setting '$name' to '$value' ";
        $this->data[$name] = $value;
    }

    public function __get($name) {
        echo "Getting '$name' ";
        if (array_key_exists($name, $this->data)) {
            return $this->data[$name];
        }

        $trace = debug_backtrace();
        trigger_error(
            'Undefined property via __get(): ' . $name .
            ' in ' . $trace[0]['file'] .
            ' on line ' . $trace[0]['line'],
            E_USER_NOTICE);
        return null;
    }

    /**  PHP 5.1.0之后版本 */
    public function __isset($name) {
        echo "Is '$name' set? ";
        return isset($this->data[$name]);
    }

    /**  PHP 5.1.0之后版本 */
    public function __unset($name) {
        echo "Unsetting '$name' ";
        unset($this->data[$name]);
    }

    /**  非魔术方法  */
    public function getHidden() {
        return $this->hidden;
    }
}


echo "<pre class="brush:php;toolbar:false"> ";

$obj = new MemberTest;

$obj->a = 1;
echo $obj->a . " ";

var_dump(isset($obj->a));
unset($obj->a);
var_dump(isset($obj->a));
echo " ";

echo $obj->declared . " ";

echo "Let's experiment with the private property named 'hidden': ";
echo "Privates are visible inside the class, so __get() not used... ";
echo $obj->getHidden() . " ";
echo "Privates not visible outside of class, so __get() is used... ";
echo $obj->hidden . " ";
       

3.3 Method overloading

  演示一个例子：

<pre name="code">  #__call , __callStatic
class MethodTest {
    public function __call($name, $arguments) {
        // 注意: $name 区分大小写
        echo "Calling object method '$name' "
             . implode(', ', $arguments). " ";
    }

    /**  PHP 5.3.0之后版本  */
    public static function __callStatic($name, $arguments) {
        // Note: value of $name is case sensitive.
        echo "Calling static method '$name' "
             . implode(', ', $arguments). " ";
    }
}

$obj = new MethodTest;
$obj->runTest('in object context');

MethodTest::runTest('in static context');  // PHP 5.3.0之后版本

Overloading is a bit difficult to understand and needs practice!

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