Detailed explanation of php magic method comparison and use of example code

In PHP, methods starting with two underscores are called magic methods. These methods play a decisive role in PHP.

construct() and destruct()

Constructor function and destructor should be familiar, they are used in object creation and destruction is called when. 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 are executing 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()

The 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 you cannot throw an exception 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);
 }
}
?>

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