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In PHP, methods starting with two underscores __ are called magic methods. These methods play a decisive role in PHP. Magic methods include:
__construct(), class constructor
__destruct(), class destructor
__call(), calling an inaccessible object in the object Call
__callStatic() when calling a method, call
__get() when calling an inaccessible method in static mode, call
__set() when obtaining a member variable of a class ), call
__isset() when setting a member variable of a class, call
__unset() when calling isset() or empty() on an inaccessible property, call
__unset() when calling an inaccessible property Called when unset() is called.
__sleep(), when executing serialize(), this function will be called first
__wakeup(), when unserialize() is executed, this function will be called first
__toString( ), the response method when the class is treated as a string
__invoke(), the response method when calling an object by calling a function
__set_state(), when calling var_export() to export a class, This static method will be called.
__construct() and __destruct()
The constructor and destructor should be familiar to them. Called when objects are created and destroyed. For example, we need to open a file, open it when the object is created, and close it when the object dies.
<?php class FileRead { protected $handle = NULL; function __construct(){ $this->handle = fopen(...); } function __destruct(){ fclose($this->handle); } } ?>
These two methods can be expanded when inheriting, for example:
<?php class TmpFileRead extends FileRead { function __construct(){ parent::__construct(); } function __destruct(){ parent::__destruct(); } } ?>
__call() and __callStatic( )
These two methods will be called when an inaccessible method is called in the object, and the latter is a static method. These two methods may be used in variable method (Variable functions) calls.
<?php class MethodTest { public function __call ($name, $arguments) { echo "Calling object method '$name' ". implode(', ', $arguments). "\n"; } public static function __callStatic ($name, $arguments) { echo "Calling static method '$name' ". implode(', ', $arguments). "\n"; } } $obj = new MethodTest; $obj->runTest('in object context'); MethodTest::runTest('in static context'); ?>
__get(), __set(), __isset() and __unset()
These two functions are called when get/set a member variable of a class. For example, we save the object variables in another array instead of the member variables of the object itself
<?php class MethodTest { private $data = array(); public function __set($name, $value){ $this->data[$name] = $value; } public function __get($name){ if(array_key_exists($name, $this->data)) return $this->data[$name]; return NULL; } public function __isset($name){ return isset($this->data[$name]) } public function unset($name){ unset($this->data[$name]); } } ?>
__sleep() and __wakeup()
When we execute serialize() and unserialize( ), these two functions will be called first. For example, when we serialize an object, the object has a database link. If we want to restore the link state during deserialization, we can restore the link by reconstructing these two functions. Examples are as follows:
<?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('server', 'username', 'password', 'db'); } public function __wakeup() { $this->connect(); } } ?>
__toString()
Response method when the object is treated as a string. For example, use echo $obj; to output an object
<?php // Declare a simple class class TestClass { public function __toString() { return 'this is a object'; } } $class = new TestClass(); echo $class; ?>
This method can only return a string, and an exception cannot be thrown in this method, otherwise a fatal error will occur.
__invoke()
The response method when calling an object by calling a function. As follows
<?php class CallableClass { function __invoke() { echo 'this is a object'; } } $obj = new CallableClass; var_dump(is_callable($obj)); ?>
__set_state()
When calling var_export() to export a class, this static method will be called.
<?php class A { public $var1; public $var2; public static function __set_state ($an_array) { $obj = new A; $obj->var1 = $an_array['var1']; $obj->var2 = $an_array['var2']; return $obj; } } $a = new A; $a->var1 = 5; $a->var2 = 'foo'; var_dump(var_export($a)); ?>
__clone()
Called when the object copy is completed. For example, in the singleton mode implementation method mentioned in the article Detailed Explanation of Design Patterns and PHP Implementation: Singleton Mode, this function is used to prevent objects from being cloned.
<?php public class Singleton { private static $_instance = NULL; // 私有构造方法 private function __construct() {} public static function getInstance() { if (is_null(self::$_instance)) { self::$_instance = new Singleton(); } return self::$_instance; } // 防止克隆实例 public function __clone(){ die('Clone is not allowed.' . E_USER_ERROR); } } ?>
Magic constants
Most of the constants in PHP are unchanged, but there are 8 constants that will change as their location in the code changes. These 8 A constant is called a magic constant.
__LINE__, the current line number in the file
__FILE__, the full path and file name of the file
__DIR__, the directory where the file is located
__FUNCTION__, function Name
__CLASS__, class name
__TRAIT__, Trait name
__METHOD__, class method name
These magic constants are often used to obtain current environment information or record logs.
The above is the entire content of this article, I hope it will be helpful to everyone's study.
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