public function swap()
    {
        $first = $this->first;
        $this->first = $this->second;
        $this->second = $first;
        return $this;
    }
public function swap()
    {
        $first = $this->first;
        $this->first = $this->second;
        $this->second = $first;
        return $this;
    }
public function swap ( ) { $ first = $ this -> first ; $ this -> first = $ this -> second ; $ this -> second = $ first ; return $ this ; }
Swaps first and second.

@return $this
Swaps first and second .