How to use $this inside php closure?

I have code like this:

class Foo {

   var $callbacks = array();
   function __construct() {
      $this->callbacks[] = function($arg) {
         return $this->bar($arg);
      };
   }
   function bar($arg) {
      return $arg * $arg;
   }
}

and I would like to use $this inside closures, I've try to add use ($this) but this throw error:

Cannot use $this as lexical variable

Answer

You cannot use $this as this is an explicit reserved variable for the class inside reference to the class instance itself. Make a copy to $this and then pass it to the use language construct.

class Foo {

   var $callbacks = array();
   function __construct() {
      $class = $this;
      $this->callbacks[] = function($arg) use ($class) {
         return $class->bar($arg);
      };
   }
   function bar($arg) {
      return $arg * $arg;
   }

}