How to recognize magic methods in php

In PHP, all class methods starting with "__", that is, two underscores, are reserved as magic methods. The magic methods in PHP include "__construct()", "__destruct()", and "__call()" , "__callStatic()" and so on.

The magic methods are:

1, __get, __set

These two methods are Designed for properties not declared in classes and their superclasses

__get( $property ) This method is triggered when an undefined property is called, passing the parameter the property being accessed Name

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

There is no declaration here Including attributes whose access control is protected and private (that is, attributes that do not have 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 attribute.

Same as the __get method and __set method. The no declaration here includes that when called with an object, the access control is protected, private. Attributes (that is, attributes that do not have permission to access)

3. __call

__call( $method, $arg_array ) When calling an undefined method, this method is called

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 it does not exist in this class, If the __call() method exists, go to the __call() method in the parent class

4. __autoload

__autoload function, it will try to use the __autoload function that has not been defined yet Automatically called when the class. 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:

The code is as follows:

<?php   
class Loader   
{   
static function autoload_class($class_name)   
{   
//寻找正确的$class_name类，并引入，没有则抛出异常   
}   
}   
/**
*   设置对象的自动载入
*   spl_autoload_register — Register given function as __autoload() implementation
*/   
spl_autoload_register(array(&#39;Loader&#39;, &#39;autoload_class&#39;));   
$a = new Test();//Test没用require就实例化，实现自动加载，很多框架就用这种方法自动加载类   
?>

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 method, this method is called when an object is created. The advantage of using this method compared to PHP4 is that the constructor method can have a unique name. No matter what the name of the class it is in is. In this way, when you change the name of the class, you do not need to change the name of the constructor method

__destruct destructor method. PHP will remove the object from memory before it is destroyed. Before clearing) call this method. 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.

In the namespace of a function, this will happen 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 PHP5 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, some initialization operations need to be performed. , can be implemented in the __clone method.

7, __toString

__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 can only take effect when used in conjunction with echo() or print(). After PHP 5.2.0, it can take effect 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 is used during serialization

__wakeup is called during deserialization

serialize() Check the class Is there a function with the magic name __sleep. 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. In addition, this function is also useful if you have very large objects that do not need to be stored completely.

Conversely, 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 re-establish any database connections that may have been lost during serialization and to handle other re-initialization tasks.

9, __set_state

When var_export() is called, this static method will be 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

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

PHP5.3.0 or above is valid

11. __callStatic

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

Valid for PHP5.3.0 or above

PHP has indeed strengthened 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

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