Magic Methods in PHP5_PHP Tutorial

From PHP 5 onwards, classes in PHP can use magic methods. It stipulates that methods starting with two underscores (__) are reserved as magic methods, so it is recommended that function names do not start with __ unless it is to overload an existing magic method.

1. __get, __set

These two methods are designed for properties that are not declared in the class and their parent class.

　◆__get( $property ) This method will be triggered when an undefined property is called, and the parameter passed is the name of the property being accessed.

　◆__set( $property, $value ) When assigning a value to an undefined property, this method will be triggered, and the parameters passed are the property name and value to be set.

The non-declarations here include attributes whose access control is protected and private (that is, attributes that have no permission to access) when called using objects.

2. __isset, __unset

　◆__isset( $property ) This method is called when the isset() function is called on an undefined property.

　◆__unset( $property ) This method is called when the unset() function is called on an undefined property.

Same as the __get method and __set method, the undeclared here includes attributes whose access control is protected and private (that is, attributes that have no permission to access) when called using an object.

3. __call

　__call( $method, $arg_array ) This method is called when calling an undefined method.

The undefined methods here include methods that do not have permission to access; if the method does not exist, go to the parent class to find the method. If it does not exist in the parent class, call the __call() method of this class. If the __call() method does not exist in this class, go to the __call() method in the parent class.

4. __autoload

__autoload function, which is automatically called when trying to use a class that has not been defined yet. By calling this function, the scripting engine has a last chance to load the required classes before PHP fails with an error.

If you want to define a global autoloading class, you must use the spl_autoload_register() method to register the processing class to the PHP standard library:

[php]

class Loader

{                                                  

static function autoload_class($class_name) {                                                            

//Find the correct $class_name class and introduce it, if not, an exception will be thrown.

}                                                                      

}

/**

* Set up automatic loading of objects

* spl_autoload_register — Register given function as __autoload() implementation

*/

spl_autoload_register(array(‘Loader’, ‘autoload_class’));

$a = new Test();//Test is instantiated without require to achieve automatic loading. Many frameworks use this method to automatically load classes

class Loader

{                                              

static function autoload_class($class_name) {                                                        

//Find the correct $class_name class and introduce it, if not, an exception will be thrown

}  

}

/**

* Set up automatic loading of objects

* spl_autoload_register — Register given function as __autoload() implementation

*/

spl_autoload_register(array(‘Loader’, ‘autoload_class’));

$a = new Test();//Test is instantiated without require to achieve automatic loading. Many frameworks use this method to automatically load classes

Note: Exceptions thrown in the __autoload function cannot be caught by the catch statement block and cause fatal errors, so they should be caught in the function itself.

5. __construct, __destruct

　◆__construct constructor, this method is called when an object is created. The advantage of using this method compared to PHP4 is that the constructor can have a unique name, no matter what the name of the class it is in. In this way, you When you change the name of a class, you don't need to change the name of the constructor.

　◆__destruct destructor method, PHP will call this method before the object is destroyed (that is, before it is cleared from memory). By default, PHP only releases the memory occupied by object properties and destroys object-related resources. The destructor allows you to execute arbitrary code to clear memory after using an object. When PHP decides that your script is no longer associated with the object, the destructor will be called.

Within a function’s namespace, this happens when the function returns. For global variables, this happens at the end of the script. If you want to explicitly destroy an object, you can assign any other value to the variable pointing to the object. Usually assign the variable to NULL or call unset.

6. __clone

Object assignment in PHP 5 uses reference assignment. If you want to copy an object, you need to use the clone method. When calling this method, the object will automatically call the __clone magic method. If the object is copied, certain initialization operations need to be performed. , can be implemented in the __clone method.

7.__toString

The __toString method is automatically called when converting an object into a string, such as when using echo to print the object.

If the class does not implement this method, the object cannot be printed through echo, otherwise it will display: Catchable fatal error: Object of class test could not be converted to string in, this method must return a string.

Before PHP 5.2.0, the __toString method could only take effect when used in conjunction with echo() or print(). After PHP 5.2.0, it can be used in any string environment (for example, through printf(), using the %s modifier), but cannot be used in non-string environments (such as using the %d modifier). From PHP 5.2.0, if an object that does not define the __toString method is converted to a string, an E_RECOVERABLE_ERROR error will be reported.

8. __sleep, __wakeup

　◆__sleep Use

when serializing

　◆__wakeup is called during deserialization

　serialize() checks whether there is a function with the magic name __sleep in the class. If so, the function will run before any serialization. It clears the object and should return an array containing the names of all variables in the object that should be serialized.

The purpose of using __sleep is to close any database connections the object may have, submit pending data, or perform similar cleanup tasks. Additionally, this function is useful if you have very large objects that do not need to be stored completely.

In contrast, unserialize() checks for the existence of a function with the magic name __wakeup. This function can reconstruct any resources the object may have, if present. The purpose of using __wakeup is to reestablish any database connections that may have been lost during serialization and to handle other reinitialization tasks.

9. __set_state

This static method will be called when var_export() is called (valid since PHP 5.1.0).

The only parameter of this method is an array, which contains class properties arranged in the format of array('property' => value, ...).

10. __invoke (valid for PHP 5.3.0 or above)

When trying to call an object by calling a function, the __invoke method is automatically called.

11. __callStatic (valid for PHP 5.3.0 or above)

It works similar to the __call() magic method, __callStatic() is to handle static method calls.

PHP does tighten the definition of the __callStatic() method; it must be public and must be declared static. Likewise, the __call() magic method must be defined as public, as must all other magic methods

http://www.bkjia.com/PHPjc/477768.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/477768.htmlTechArticleFrom PHP 5 and later, classes in PHP can use magic methods. It stipulates that methods starting with two underscores (__) are reserved as magic methods, so it is recommended that you do not use function names...