Detailed explanation of examples of overloading and magic methods in php-PHP Tutorial-php.cn

Detailed explanation of examples of overloading and magic methods in php

黄舟

Release： 2023-03-16 21:32:01

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Definition: PHP reserves all class methods starting with (two underscores) as magic methods. Therefore, when defining class methods, except for the above magic methods, it is recommended not to be prefixed with .

Function: The pattern method can be used to easily realize overloading in PHP object-oriented (Overloading is to dynamically create classesAttributes and methods )

In fact, many bloggers have already written these methods...but I still want to say it again. . Who asked you to come and listen? It’s not easy to finish reading so many words before leaving!

1.construct, destruct
constuct is called when constructing the object;
destruct is called when the object is explicitly destroyed or the script ends;

class Foo {    
private $name;    
private $link;    
public function construct($name) {        
$this->name = $name;
    }    
    public function destruct() {        
    echo &#39;Destroying: &#39;, $this->name, PHP_EOL;//PHP_EOL代表php的换行符    }
}

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Stop , let’s start with a wave of definitions and usage of overloading:

Definition: "Overloading" provided by PHP (overloading) refers to dynamically "creating" class attributes and methods. (We achieve this through magic methods)

Function: When calling undefined or invisible class attributes or methods in the current environment , the overloaded method will be called. "Inaccessible properties" and "Inaccessible methods" will be used later to refer to these undefined or invisible class properties or methods.

Note: All overloaded methods must be declared public.

2.get, set, isset, unset, call, callStatic //Why are they put together?

set is called when assigning a value to an inaccessible or non-existent property
get is called when reading an inaccessible or non-existent property

isset is not accessible Or a non-existent property is called when isset() or empty() is called
unset is called when an inaccessible or non-existent property is unset

call is called when an inaccessible or non-existent method is called Call
callStatic is called when calling an inaccessible or non-existent static method

Example #1 Use get(), set(), isset() and unset() for attribute overloading

<?php
class PropertyTest {
     /**  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, $value) 
    {
        echo "Setting &#39;$name&#39; to &#39;$value&#39;\n";
        $this->data[$name] = $value;
    }


    public function get($name) 
    {
        echo "Getting &#39;$name&#39;\n";
        if (array_key_exists($name, $this->data)) {
            return $this->data[$name];
        }

        $trace = debug_backtrace();
        trigger_error(
            &#39;Undefined property via get(): &#39; . $name .
            &#39; in &#39; . $trace[0][&#39;file&#39;] .
            &#39; on line &#39; . $trace[0][&#39;line&#39;],
            E_USER_NOTICE);
        return null;
    }



    /**  PHP 5.1.0之后版本 */
    public function isset($name) 
    {
        echo "Is &#39;$name&#39; set?\n";
        return isset($this->data[$name]);
    }

    /**  PHP 5.1.0之后版本 */
    public function unset($name) 
    {
        echo "Unsetting &#39;$name&#39;\n";
        unset($this->data[$name]);
    }

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


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

$obj = new PropertyTest;

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

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

echo $obj->declared . "\n\n";

echo "Let&#39;s experiment with the private property named &#39;hidden&#39;:\n";
echo "Privates are visible inside the class, so get() not used...\n";
echo $obj->getHidden() . "\n";
echo "Privates not visible outside of class, so get() is used...\n";
echo $obj->hidden . "\n";
?>

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Have you finished reading? looks great!

5.sleep, wakeup
sleep is called when using serialize, useful when you don’t need to save all the data of a large object

wakeup when using Called when unserialize, can be used to do some object initialization operations

<?php
class Connection 
{
    protected $link;
    private $server, $username, $password, $db;
    
    public function construct($server, $username, $password, $db)
    {
        $this->server = $server;
        $this->username = $username;
        $this->password = $password;
        $this->db = $db;
        $this->connect();
    }
    
    private function connect()
    {
        $this->link = mysql_connect($this->server, $this->username, $this->password);
        mysql_select_db($this->db, $this->link);
    }
    
    public function sleep()
    {
        return array(&#39;server&#39;, &#39;username&#39;, &#39;password&#39;, &#39;db&#39;);
    }
    
    public function wakeup()
    {
        $this->connect();
    }
}
?>

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6.clone

Called when the object is cloned, used to adjust the object Clone behavior

<?php
class SubObject
{
    static $instances = 0;
    public $instance;

    public function construct() {
        $this->instance = ++self::$instances;
    }

    public function clone() {
        $this->instance = ++self::$instances;
    }
}

class MyCloneable
{
    public $object1;
    public $object2;

    function clone()
    {
      
        // 强制复制一份this->object， 否则仍然指向同一个对象
        $this->object1 = clone $this->object1;
    }
}

$obj = new MyCloneable();

$obj->object1 = new SubObject();
$obj->object2 = new SubObject();

$obj2 = clone $obj;


print("Original Object:\n");
print_r($obj);

print("Cloned Object:\n");
print_r($obj2);

?>

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7.toString
Called when a class is converted to a string

<?php
class SubObject
{
    static $instances = 0;
    public $instance;

    public function construct() {
        $this->instance = ++self::$instances;
    }

    public function clone() {
        $this->instance = ++self::$instances;
    }
}

class MyCloneable
{
    public $object1;
    public $object2;

    function clone()
    {
      
        // 强制复制一份this->object， 否则仍然指向同一个对象
        $this->object1 = clone $this->object1;
    }
}

$obj = new MyCloneable();

$obj->object1 = new SubObject();
$obj->object2 = new SubObject();

$obj2 = clone $obj;


print("Original Object:\n");
print_r($obj);

print("Cloned Object:\n");
print_r($obj2);

?>

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8.set_state
This static method is called when var_export() is called to export a class. Use the return value of set_state as the return value of var_export.

<?php

class A
{
    public $var1;
    public $var2;

    public static function set_state($an_array) // As of PHP 5.1.0
    {
        $obj = new A;
        $obj->var1 = $an_array[&#39;var1&#39;];
        $obj->var2 = $an_array[&#39;var2&#39;];
        return $obj;
    }
}

$a = new A;
$a->var1 = 5;
$a->var2 = &#39;foo&#39;;

eval(&#39;$b = &#39; . var_export($a, true) . &#39;;&#39;); // $b = A::set_state(array(
                          //    &#39;var1&#39; => 5,
                          //    &#39;var2&#39; => &#39;foo&#39;,
                          // ));
var_dump($b);
?>

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