class Weight
{
  protected $weight;

  public function __construct($weight)
  {
    $this->weight = $weight;
  }

  public function gain($kilograms)
  {
    return new static($this->weight + $kilograms);
  }


  public function loose($kilograms)
  {
    return new static($this->weight - $kilograms);
  }


}

class GymMember
{
  protected $name;
  protected $weight;


  public function __construct($name, Weight $weight)
  {
    $this->name = $name;
    $this->weight = $weight;
  }


  public function workoutFor(TimeLength $length)
  {

    if(!$length->inSeconds() > (40 * 60 ))
    {
      return 'Keep up the good work!';
    }

    $this->weight->loose(2);

  }

}

class TimeLength
{

  protected $seconds;


  private function __construct($seconds)
  {
    $this->seconds = $seconds;
  }


  public static function Minutes($minutes)
  {
    return new static($minutes * 60);
  }


  public function inSeconds()
  {
    return $this->seconds;
  }


  public function inMinutes()
  {
    return $this->seconds / 60;
  }


  public function inHours()
  {
    return $this->seconds / 60 / 60;
  }

}

$gymMember = new GymMember('MTROBERT', new Weight(78));

$gymMember->workOutFor(Timelength::minutes(45));



var_dump($gymMember);

public function workoutFor(TimeLength $length)
  {

    // ...

    $this->weight->loose(2);

  }

$this->weight = $this->weight->loose(2);

public function loose($kilograms)
{
   $this->weight -= $kilograms;
}