The Magic method in PHP

PHP Magic Method:

__construct (), __destruct (), __call (), __callstatic (), __get (), __set (), __isset (), __unset (), __sleep (), __wakeup (), __ ToString (), __invoke (), __set_state (), __clone (), and __debuginfo () are known in PHP as "Magic Methods" (Magic methods). You cannot use these method names when naming your own class methods, unless you want to use their magic features.

__construct (), the class's constructor __destruct (), the class's destructor __call (), calls an inaccessible method in the object (private or nonexistent) when called __callstatic (), invokes a non-accessible method in a static manner when called __ Get (), which gets a member variable of a class when called __set (), sets a member variable of a class when called __isset (), when calling Isset () or empty () on a non-accessible property call __unset () when called unset () on an inaccessible property. __sleep (), when executing serialize (), first calls this function __wakeup (), executes Unserialize (), first calls the function __tostring (), the class is treated as a string when the response method __invoke (), This static method is called when the function is called when an object is called by the Response Method __set_state (), when the Var_export () export class is called. __clone (), called when the object copy is complete

__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 ' in the constructor <br> ';    } function __destruct () {echo ' in destructor <br> '; }} $val = new ConDes (); unset ($val);? ><pre name= "code" class= "PHP" >

Output:

In a constructor, in a destructor

Both methods are called when __call () and __callstatic () call an inaccessible method in an object, which is a static method.

<?php class Methodtest {public Function __call ($name, $arguments) {var_dump ($arguments); Echo "Object method $name and". Implode (', ', $arguments). "    <br> "; The public static function __callstatic ($name, $arguments) {echo "static method $name and". Implode (', ', $argumen TS). "    <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 you get an inaccessible class member variable or when you set an inaccessible class member variable.

<?phpclass 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 are called first. For example, when we serialize an object that has a database link that wants to restore the link state in deserialization, you can refactor the two functions to achieve a link recovery.

<?phpclass 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 () &NBSP;&Nbsp;  {    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:

array (size=4)
  0 => string ‘1‘ (length=1)
  ‘id‘ => string ‘1‘ (length=1)
  1 => string ‘m0sh1‘ (length=5)
  ‘username‘ => string ‘m0sh1‘ (length=5)
sleep
wakeup
object(Connection)[2]
  public ‘link‘ => resource(6, mysql link)
  private ‘server‘ => string ‘localhost‘ (length=9)
  private ‘username‘ => string ‘moshi‘ (length=4)
  private ‘password‘ => string ‘moshi‘ (length=5)
  private ‘db‘ => string ‘test‘ (length=4)
array (size=4)
  0 => string ‘1‘ (length=1)
  ‘id‘ => string ‘1‘ (length=1)
  1 => string ‘m0sh1‘ (length=5)
  ‘username‘ => string ‘m0sh1‘ (length=5)




__toString()

对象当成字符串时的回应方法。例如使用echo $obj;

<?php  class TestClass  {public    function __tostring () {        return ' This is a object ';    }} $class = new TestClass (); Echo $class;  ? >

Output:

This is a object

This method can only return a string, and cannot throw an exception in this method, or a fatal error will occur.

__invoke ()

A method of responding when invoking an object in a way called a function.

<?phpclass invoke{public function __invoke () {echo ' in invoke<br> ';}} Class noinvoke{} $obj = new Invoke (), $obj (), Var_dump (Is_callable ($obj)), $obj 2 = new Noinvoke ();//$obj 2 (); Var_dump (Is_ Callable ($obj 2));

Output:

In Invoke
Boolean true
Boolean false

__set_state ()

This static method is called when the Var_export () export class is called.

<?php  class A  {public    $var 1;    Public $var 2;public static function __set_state ($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 complete.

<?php  class Singleton {      private static $_instance = NULL;    Private constructor Method     __construct () {} public    static function getinstance () {        if (Is_null (self::$_ Instance) {            self::$_instance = new Singleton ();        }        return self::$_instance;    }    Prevent clone instance public    function __clone () {die        (' clone was 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 Magic method in PHP