php - Cannot use invoke magic method within another object -

i have experienced think it's bug, i'm not sure. come here ask people know more me, is php bug? @ following lines:

<h1>tests</h1>  <?php class foo   {   public function __invoke()     {     return 'called correctly';     }   }  class boo   {   public function __construct()     {     $this->foo = new foo();     }   }  $foo = new foo(); echo $foo();  echo "<br><br><hr><br><br>";  $boo = new boo(); echo $boo->foo(); 

according the specification, since the __invoke() method called when script tries call object function, should obtain this:

called correctly

---

called correctly

but last echo not executed. instead, this:

php fatal error: call undefined method boo::foo() in [...]/index.php on line 26

is bug or expected behaviour? if it's bug, how submit highly appreciated.

edit based on jon answer show further ugly behaviour

class doo   {   public function __construct()     {     // foo class same 1 defined before      $test = new foo();     echo $test();      // echos correctly      echo "<br><br><hr><br><br>";      $this->foo = $test;     echo $this->foo();  // error. heisenbehaviour?     }   }  $boo = new doo(); 

it not bug, , not limited foo being object defines __invoke. same error callable:

class foo {     private $bar = 'rand';      public function __construct()     {         $this->bar(); // won't work     }   } 

you need either write 2 lines, or use call_user_func:

// #1 $boo = new boo(); $foo = $boo->foo; $foo();  // #2 $boo = new boo(); call_user_func($boo->foo);