php - preg_match not accepting $this -

am being stupid or preg_match() not accept global class variables?

class test{     private$username,$usernamevalidation;     public function __construct($username){         $this->username=$username;         $this->usernamevalidation="/^[a-za-z0-9]{0,8}$/";     }     public function validate(){        if(!preg_match($this->usernamevalidation,$this->username)){            //failed;        }     } } 

every time compile function this, seems tell me the expression empty. seems work preg_match("/^[a-za-z0-9]{0,8}$/",$this->username);.

you can try keeping regex assignment @ class level:

class test {     const usernamevalidation = '/^[a-za-z0-9]{0,8}$/';     private $username;      public function __construct($username){         $this->username=$username;     }     public function validate(){        if(!preg_match(usernamevalidation, $this->username)) {            //failed;        }     } }