Examples of magic methods in PHP

What is a magic method?

In the PHP object-oriented, provides a series of magic methods, these magic methods for our programming provides a lot of convenience, PHP in the beginning of the two underscore __ method is called Magic method, these magic methods do not need to display the call but a certain conditions to start. This chapter will give you a quick look at the magic methods available in PHP.

The Magic method of PHP is the following table:

Function	Description
__construct ()	Constructors for classes
__destruct ()	Destructors for classes
__call ()	Called when an inaccessible method is called in an object
__callstatic ()	Called when a non-accessible method is called in a static way
__get ()	Called when a member variable of a class is obtained
__set ()	Called when a member variable of a class is set
__isset ()	Called when isset () or empty () is called on an inaccessible property
__unset ()	Called when unset () is called on a non-accessible property.
__sleep ()	When executing serialize (), this function is called first
__wakeup ()	When executing unserialize (), this function is called first
__tostring ()	A method of responding when a class is treated as a string
__invoke ()	Method of responding when calling an object in a way called a function
__set_state ()	This static method is called when the Var_export () export class is called.
__clone ()	Called when the object copy is complete

"__" in the table above is two underline, not a "_"

Let's take a look at some examples of these magic methods

__construct () and __destruct ()

Constructors and destructors should be unfamiliar, and they are called when objects are created and extinct. For example, we need to open a file, open when the object is created, close when the object dies

<?phpclass fileread{    protected $handle = NULL;    function __construct () {        $this->handle = fopen (...);    }    function __destruct () {        fclose ($this->handle);    }}? >

These two methods can be extended during inheritance, for example:

<?phpclass Tmpfileread extends fileread{    function __construct () {        parent::__construct ();    }    function __destruct () {        parent::__destruct ();    }}? >

__call () and __callstatic ()

These two methods are called when an inaccessible method is called in an object, which is a static method. These two methods may be used in the variable method (Variable functions) call.

<?phpclass 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 an object variable in another array, not the member variable of the object itself.

<?phpclass 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 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.

Examples are as follows:

<?phpclass 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 ()

The method that the object responds to as a string. For example, use echo $obj to output an object

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

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. As follows

<?phpclass callableclass{    function __invoke () {        echo ' This is a object ';    }} $obj = new Callableclass;var_dump (is_callable ($obj));? >

__set_state ()

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

<?phpclass a{public    $var 1;    Public $var 2;    public static function __set_state ($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 complete. For example, in the design pattern in detail and the implementation of PHP: Singleton mode in the article mentioned in the implementation of the Singleton mode, using this function to prevent the object from being cloned.

<?phppublic 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;    }    Prevents the clone instance public    function __clone () {die        (' clone was not allowed. '). E_user_error);}    }? >