Exploring PHP magic functions: __sleep()

__sleep() is a special magic function in PHP that is called when an object is serialized. When we need to serialize an object into a string and save it to a file or pass it to other systems, PHP automatically calls the __sleep() function. This article will delve into the usage and mechanism of the __sleep() function.

The principle of __sleep() function

When PHP needs to serialize an object into a string, it will first check whether the __sleep() function is defined on the object. If it is defined, then PHP will first call the __sleep() function and perform the operations therein, and then perform the serialization operation. The return value of the __sleep() function must be an array containing the names of the attributes that need to be serialized.

For example, we define a Person object, which contains two attributes: name and age. The code is as follows:

class Person {  
    public $name;  
    public $age;  
    public function __construct($name, $age) {  
        $this->name = $name;  
        $this->age = $age;  
    }  
    public function __sleep() {  
        return array('name', 'age');  
    }  
}  

$person = new Person('张三', 20);  
$str = serialize($person);  
var_dump($str);

In the above code, we rewrite the __sleep() function, specifying Two attributes, name and age, need to be serialized. When we call the serialize() function to serialize the $person object into a string, PHP will automatically call the __sleep() function and return an array containing name and age.

__sleep() function notes

1. __sleep() function must return an array. If it is not an array, an E_NOTICE warning will be thrown, and the serialization operation will fail.
2. __sleep() function can return an empty array, which means that no attributes need to be serialized, which may be useful in some scenarios.
3. If the array returned by the __sleep() function contains an undefined attribute, an E_NOTICE warning will be thrown and the attribute will be ignored.
4. If the __sleep() function is defined in an object but the __wakeup() function is not defined, all attributes of the object will be cleared during deserialization.

Application scenarios of __sleep() function

#__sleep() function can be used to control the attributes that need to be serialized when object serialization, which can be excluded in the __sleep() function Certain properties are used to protect sensitive data or improve serialization performance in some cases.

For example, in a User object with a password, in order to protect user privacy, we do not want to serialize the password attribute to a file or pass it to other systems. We can override the __sleep() function. Exclude this attribute:

class User {  
    public $name;  
    public $password;  
    public function __construct($name, $password) {  
        $this->name = $name;  
        $this->password = $password;  
    }  
    public function __sleep() {  
        return array('name');  
    }  
}  

$user = new User('张三', '123456');  
$str = serialize($user);  
var_dump($str);

In the above code, we exclude the password attribute and it will not be serialized to the file or passed to other systems.

Summary

In PHP, the __sleep() function is a very useful magic function. It can control the attributes that need to be serialized when the object is serialized, and can protect the security of sensitive data. Or improve serialization performance. When using the __sleep() function, you need to note that the return value must be an array containing the attributes that need to be serialized, otherwise the serialization operation will fail. If the __sleep() function is defined in an object but the __wakeup() function is not defined, all attributes of the object will be cleared during deserialization and should be defined as needed.

The above is the detailed content of Exploring PHP magic functions: __sleep(). For more information, please follow other related articles on the PHP Chinese website!