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magic method in php
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- 2016-08-08 09:30:101156browse
PHP magic methods:
__construct(), __destruct(), __call(), __callStatic(), __get(), __set(), __isset(), __unset(), __sleep(), __wakeup(), Methods such as __toString(), __invoke(), __set_state(), __clone() and __debugInfo() are called "Magic methods" in PHP. You cannot use these method names when naming your own class methods unless you want to use their magic functionality.
__construct()，类的构造函数 __destruct()，类的析构函数 __call()，在对象中调用一个不可访问方法(私有或者不存在)时调用 __callStatic()，用静态方式中调用一个不可访问方法时调用 __get()，获得一个类的成员变量时调用 __set()，设置一个类的成员变量时调用 __isset()，当对不可访问属性调用isset()或empty()时调用 __unset()，当对不可访问属性调用unset()时被调用。 __sleep()，执行serialize()时，先会调用这个函数 __wakeup()，执行unserialize()时，先会调用这个函数 __toString()，类被当成字符串时的回应方法 __invoke()，调用函数的方式调用一个对象时的回应方法 __set_state()，调用var_export()导出类时，此静态方法会被调用。 __clone()，当对象复制完成时调用
__construct() and __destruct()
The constructor __construct() is called when the object is created, and the destructor __destruct() is called when the object dies
<?php  
class ConDes
{
    protected $a = '';
    function __construct(){
        echo '在构造函数中<br>';
}
function __destruct(){
echo '在析构函数中<br>';
}
}
$val = new ConDes();
unset($val);
?><pre name="code" class="php"> output:
In the constructor and in the destructor
__call() and __callStatic() are called when an inaccessible method is called in the object. The latter is a static method.
<?php  
class MethodTest  
{
    public function __call ($name, $arguments) {
    var_dump($arguments);
        echo "object method $name and ".implode(',',$arguments)."<br>";
}
public static function __callStatic ($name, $arguments) {
echo "static method $name and ".implode(',',$arguments)."<br>";
}
}
$obj = new MethodTest;
$obj->runTest('in object context','another arg');
MethodTest::runTest('in static context');
?> output:
array (size=2)
0 => string 'in object context' (length=17)
1 => string 'another arg' (length=11)
object method runTest and in object context,another arg
static method runTest and in static context
__get(), __set(), __isset() and __unset()
These two functions are called when getting an inaccessible class member variable or setting an inaccessible class member variable .
<?php class MethodTest
{
private $data = array();
private $a = '';
public $bbb = '';
public function __set($name, $value){
$this->data[$name] = $value;
echo '__set';
var_dump($this->data);
}
public function __get($name){
echo '__get';
var_dump($this->data);
if(array_key_exists($name, $this->data))
return $this->data[$name];
return NULL;
}
public function __isset($name){
echo '__isset';
return isset($this->data[$name]);
}
public function __unset($name){
echo '__unset';
unset($this->data[$name]);
}
}
$in = new MethodTest();
$in->a = 'aaaa';
$aaa = $in->a;
$res = isset($in->c)? 'set':'not set';
echo '<br>'.$res.'<br>';
unset($in->a);
?> output:
__set
array (size=1)
'a' => string 'aaaa' (length=4)
__get
array (size=1)
'a' => string 'aaaa' (length=4)
__isset
not set
__unset
__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.
<span></span>
<?php class Connection {
    public $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()
{
echo 'sleep<br>';
return array('server', 'username', 'password', 'db');
}
public function __wakeup()
{
echo 'wakeup<br>';
$this->connect();
}
}
$a = new Connection('localhost','mosi','moshi','test');
$sql = 'select id,username from user limit 1';
$res = mysql_query($sql,$a->link);
$res = mysql_fetch_array($res);
var_dump($res);
$sres = serialize($a);
mysql_close($a->link);
//unset($a);
$unsres = unserialize($sres);
var_dump($unsres);
$sql = 'select id,username from user limit 1';
$ress = mysql_query($sql,$unsres->link);
$ress = mysql_fetch_array($ress);
var_dump($ress);
?> output:
<span>array (size=4)<br> 0 => string '1' (length=1)<br> 'id' => string '1' (length=1)<br> 1 => string 'm0sh1' (length =5)<br> 'username' => string 'm0sh1' (length=5)<br>sleep<br>wakeup<br>object(Connection)[2]<br> public 'link' => resource(6, mysql link)<br> private 'server ' => string 'localhost' (length=9)<br> private 'username' => string 'moshi' (length=4)<br> private 'password' => string 'moshi' (length=5)<br> private ' db' => string 'test' (length=4)<br>array (size=4)<br> 0 => string '1' (length=1)<br> 'id' => string '1' (length=1 )<br> 1 => string 'm0sh1' (length=5)<br> 'username' => string 'm0sh1' (length=5)</span>
<span>__toString()<br> when the object is treated as a string response method. For example, using echo $obj;</span>
<span></span>
<?php class TestClass
{
public function __toString() {
return 'this is a object';
}
}
$class = new TestClass();
echo $class;
?> output:
<span></span><span></span>this is a object
This method can only return a string, and exceptions cannot be thrown in this method, otherwise a fatal error will occur.
__invoke()
The response method when calling an object by calling a function.
<?php class Invoke{
public function __invoke(){
echo 'in invoke<br>';
}
}
class noInvoke{
}
$obj = new Invoke();
$obj();
var_dump(is_callable($obj));
$obj2 = new noInvoke();
//$obj2();
var_dump(is_callable($obj2));Output:
in invoke
boolean true
boolean false
__set_state()
This static method will be called when var_export() is called to export a class.
<?php class A
{
public $var1;
public $var2;
public static function __set_state ($arr) {
$obj = new A;
$obj->var1 = 'var11';
$obj->var2 = $arr['var2'];
return $obj;
}
}
$a = new A;
$a->var1 = 5;
$a->var2 = 'foo';
var_dump($a);
var_export($a);
eval('$ress = '.var_export($a,true).';');
var_dump($ress);
?>Output:
object(A)[1]
public 'var1' => int 5
public 'var2' => string 'foo' (length=3)
A::__set_state(array( 'var1' => 5, 'var2' => 'foo', ))
object(A)[2]
public 'var1' => string 'var11' (length=5)
public 'var2' => string 'foo' (length=3)
__clone()
Called when the object copy is completed.
<?php 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 error: ' . E_USER_ERROR);
}
}
$a = Singleton::getInstance();
$b = Singleton::getInstance();
if( $a === $b ){
echo 'equal<br>';
}
$c = clone $b;
?>Output:
equal
Clone is not allowed error: 256
PHP Magic Constants: Introduction here
The above has introduced the magic methods in PHP, including the relevant content. I hope it will be helpful to friends who are interested in PHP tutorials.