Magic method in PHP (Magic methods) and solid magic

Php's method of starting with two underscores is called a magic method, which plays a pivotal role in PHP.     Magic methods include: __construct (), class constructor __destruct (), Class destructor __call (), call to an inaccessible method in an object when calling __callstatic (), invoking an inaccessible method in a static way __get (), 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 calling unset () on an inaccessible property    ) is called. __sleep (), when executing serialize (), first calls the function __wakeup (), executes Unserialize (), first calls the function __tostring (), the class is treated as a string response method __invoke (), calls the function    This static method is called when an object is called in the way of a response method __set_state (), when the Var_export () export class is called. __clone (), calling __construct () and __destruct () constructors and destructors when the object is copied are not unfamiliar, 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<?PHPclassfileread{protected $handle=NULL; function__construct () {$this->handle =fopen(...); }    function__destruct () {fclose($this-handle); }}?>These two methods can be extended during inheritance, for example:<?PHPclassTmpfilereadextendsfileread{function__construct () {Parent::__construct (); }    function__destruct () {Parent::__destruct (); }}?>Both methods are called when __call () and __callstatic () call an inaccessible method in an object, which is a static method. These two methods may be used in the variable method (Variable functions) call. <?PHPclassMethodtest { Public function__call ($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=Newmethodtest;$obj->runtest (' in object context ')); Methodtest:: Runtest (' in static context ');?>__get (), __set (), __isset () and __unset () when Get/These two functions are called when a member variable of a class is set. For example, we save an object variable in another array, not the member variable of the object itself.<?PHPclassmethodtest{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:<?PHPclassConnection {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; $this-Connect (); }    Private functionConnect () {$this->link =mysql_connect($this->server,$this->username,$this-password); mysql_select_db($this-&GT;DB,$this-link); }     Public function__sleep () {return Array(' Server ', ' username ', ' password ', ' db '); }     Public function__wakeup () {$this-Connect (); }}?>the __tostring () object is used as a string response method. For example, using the Echo$obj; To output an object<?PHP//Declare a simple classclasstestclass{ Public function__tostring () {return' This is a object '; }}$class=NewTestClass ();Echo $class;?>This method can only return a string, and cannot throw an exception in this method, or a fatal error will occur. __invoke () invokes a function in a way that invokes an object when the response method is called. as follows<?PHPclassCallableclass {function__invoke () {Echo' This is a object '; }}$obj=NewCallableclass;Var_dump(is_callable($obj));?>This static method is called when __set_state () calls Var_export () to export the class. <?PHPclassa{ Public $var 1;  Public $var 2;  Public Static function__set_state ($an _array) {        $obj=NewA; $obj-&GT;VAR1 =$an _array[' Var1 ']; $obj-&GT;VAR2 =$an _array[' Var2 ']; return $obj; }}$a=NewA;$a-&GT;VAR1 = 5;$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. <?PHP Public classSingleton {Private Static $_instance=NULL; //Private Construction Methods    Private function__construct () {} Public Static functiongetinstance () {if(Is_null(Self::$_instance) ) { self::$_instance=NewSingleton (); }        returnSelf::$_instance; }    //Preventing cloned Instances     Public function__clone () { die(' Clone is not allowed. ')E_user_error); }}?>Magic Constants (Magic constants) Most of the constants in PHP are immutable, but there are 8 constants that change with the location of their code, and these 8 constants are called Magic constants. __line__, the current line number in the file__file__, the full path and filename of the file __dir__, the directory where the file resides__function__, the function name__class__, the name of the class __trait__,trait__method__, the method name of the class __namespace__, the name of the current namespace these Magic constants are often used to obtain current environment information or log logs. 

Magic method in PHP (Magic methods) and solid magic