public function add($element): bool
    {
        if ($this->contains($element)) {
            return false;
        }

        return parent::add($element);
    }
public function add($element): bool
    {
        if ($this->contains($element)) {
            return false;
        }

        return parent::add($element);
    }
public function add ( $ element ) : bool { if ( $ this -> contains ( $ element ) ) { return false ; } return parent :: add ( $ element ) ; }
Adds the specified element to this set, if it is not already present.

@param mixed $element The element to add to the set.

@return bool `true` if this set did not already contain the specified
element.

@throws InvalidArgumentException when the element does not match the
specified type for this set.
Adds the specified element to this set if it is not already present .