php - Empty function not working in CodeIgniter

if(!empty($this->input->post())){
   Var_dump($this->input-post());
}

this shows me Fatal Error

Fatal error: Can't use method return value in write context in D:\install\wamp\www\CI\application\controllers\user\user.php on line 39

I don't understand why this is happening.
In the CodeIgniter in controller file I have written this

Answer

change this

if(!empty($this->input->post())){
   Var_dump($this->input-post());
}

to

if($this->input->post()){
   var_dump($this->input-post());
}