Solution Review: Type Hinting

<?php 
interface User {
  public function setUsername($username); 
  public function getUsername();
  public function setGender($gender); 
  public function getGender(); 
}
class Commentator implements User {
  private $username = '';
  private $gender = 'Not available';
  public function setUsername($name) {
    $this -> username = (is_string($name))? $name : 'N/A';
  }
  public function getUsername() {
    return $this -> username; 
  }
  public function setGender($gender) {
    $gendersArray = array('female', 'male', 'other');
    if(in_array($gender, $gendersArray)) {
      $this -> gender = $gender;
    }
  }
  public function getGender() {
    return $this -> gender; 
  }
}
function addMrOrMrsToUsername(User $user) {
  $userName   = $user -> getUsername();
  $userGender = $user -> getGender();
  if($userGender === 'female') {
    return "Mrs. " . $userName; 
  }
  else if($userGender === 'male') {
    return "Mr. " . $userName; 
  }
  return $userName; 
}
function test()
{
  $user1 = new Commentator(); 
  $user1 -> setUsername("Jane"); 
  $user1 -> setGender("female"); 
  $user2 = new Commentator(); 
  $user2 -> setUsername("Bob"); 
  $user2 -> setGender("male");
  
  return addMrOrMrsToUsername($user1) . " and " .addMrOrMrsToUsername($user2);
}
echo test();
?>