Detailed explanation of how to use PHP magic methods

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.

__clone(), call

__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, $arguments) {
  echo "Calling object method &#39;$name&#39; ". implode(&#39;, &#39;, $arguments). "\n";
 }
 
 public static function __callStatic ($name, $arguments) {
  echo "Calling static method &#39;$name&#39; ". implode(&#39;, &#39;, $arguments). "\n";
 }
}
 
$obj = new MethodTest;
$obj->runTest(&#39;in object context&#39;);
MethodTest::runTest(&#39;in static context&#39;);
?>

__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(&#39;server&#39;, &#39;username&#39;, &#39;password&#39;, &#39;db&#39;);
 }
 
 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 &#39;this is a object&#39;;
 }
}
 
$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 &#39;this is a object&#39;;
 }
}
$obj = new CallableClass;
var_dump(is_callable($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[&#39;var1&#39;];
  $obj->var2 = $an_array[&#39;var2&#39;];
  return $obj;
 }
}
 
$a = new A;
$a->var1 = 5;
$a->var2 = &#39;foo&#39;;
var_dump(var_export($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(&#39;Clone is not allowed.&#39; . 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

__NAMESPACE__, name of current namespace

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.

For more detailed explanations on how to use PHP Magic methods, please pay attention to the PHP Chinese website!

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