Can I use a function to return a default param in php?

Question

I would like to do something like this:

function readUser($aUser = loadDefaultUser()){

 //doing read User
}

I find that it will display a erro

Answer 1

function readUser($aUser = NULL){
   if ($aUser === NULL){
        $aUser = loadDefaultUser();
   }

   //do your stuff
}