Magic methods in php classes and automatic loading of classes

__toString()： Called when trying to use the object as a string, it returns a string, similar to toString() of js objects

__invoke(): Called when an object is called as a function. like $object($a,$b) will call $object->__invoke($a,$b)

__set_state(): When var_export() is called on an object, its return value will be printed

__clone()： It is called when using the clone operation on an object and has no return value. This method can be used to modify the properties of the object obtained by clone before returning it so that the object obtained by clone can have different property values ​​​​from the object being operated on, but it cannot be returned by returning null or false to prevent the object cloning operation. The object obtained by the clone operation is not returned through the return value of this method.

Notes: The __get and __set methods can be often used to flexibly handle access to object private attributes and protected attributes. Because when a PHP object uses isset() or empty() to determine a method, it will not consider the method to be an accessible attribute (be careful if you write too much javascript. In PHP, attributes are attributes, methods are methods, and cannot be confused) When using __get, you may use isset($this->key) to judge attributes in this method, especially when you need to deal with private attributes. At this time, you should pay attention to whether __set() is defined and how to define it. To avoid misjudgment. If an object's method does not require passing parameters when calling, or the passing parameters are fixed, you can attribute the method through the __get() method, and automatically call the method in __get() and return the value.

For example, define the __get method in the class as follows:

unserialize() method: When trying to deserialize an object, this function needs to know the class of the object. If the serialization string is obtained from other ways and the class of the object is not defined in the script environment, it is required Import the file of the class. The second parameter of unserialize() is an optional callback parameter, which is used to import the file where the class is located. function importClass($calssName){ include('xxxx.php'); //File containing this class } unserialize($objstr,$callbackName);

Automatic loading of classes: __autoload()

__autoload() is a function agreed in the PHP execution environment rather than a method of a certain class. If a class is not loaded into the current file before use, the __autoload() function will be automatically called to load the class. Usually these classes The loading rules are all agreed. For example, these classes are included in files named after the class names. This method can realize on-demand loading of classes and avoid loading unnecessary classes before script execution, thereby reducing resource usage and submission performance.

Note: Errors within __autoload() cannot be caught by try-catch.

Register the function automatically called by __autoload(): The spl code base is automatically enabled by default after PHP5.0 spl_autoload_register([callback]); //Instead of writing the specific loading code in __autoload(), you can use this function to register the callback function.

If you use a class method as a callback function, you need to pass in an array: spl_autoload_register(array('class_name'|$obj,'method_name'));

For example: spl_autoload_register(array($this,'autoloadClass')); spl_autoload_register(array('YiiBase','autoload'));//Implementation of the autoloading class of the YII framework, the YiiBase class implements an autoload method. spl_autoload_register() can register multiple load functions, and all registered load functions will be tried one by one before successfully loading the class file. This is useful when different classes use different logic to import class files. spl_autoload_unregister(); //Cancel a registered load function, the parameters are the same as spl_autoload_register(). spl_autoload_functions(); // Returns all registered __autoload() functions in array

spl_autoload(class_name[,file_extensions]); //Default implementation of __autoload() function. If no function name is passed in when spl_autoload_register() is called, this function will be used by default. The execution rules of this function are: The class name is converted to lowercase as the file name, and the passed-in file_extensions (multiple extensions are separated by commas, default (.inc and .php) as the extension, try to search in the include paths set in php.ini based on the file name obtained.

spl_autoload_call(class_name);//Manually call all registered __autoload() functions to actively load class files spl_autoload_extensions([file_extentions]); //Register or return the file extensions that can be used in spl_autoload(). The extension can be in the form of .a.b, for example: spl_autoload_extentions(".class.php"); spl_autoload_register(); //Use spl_autoload() to try to automatically load class files //In this way spl_autoload('myclassName'); will try to load the file "myclassName.class.php" .