original_string: function swap (callable $fn)
    {
      $this->pack ();
      $this->data = $fn ($this->data);
      return $this;
    }
code: function swap (callable $fn)
    {
      $this->pack ();
      $this->data = $fn ($this->data);
      return $this;
    }
code_tokens: function swap ( callable $ fn ) { $ this -> pack ( ) ; $ this -> data = $ fn ( $ this -> data ) ; return $ this ; }
docstring: Replaces the current data set by another.
  
  @param callable $fn A callback that receives as argument an array of the current data and returns the
  new data array.
  @return $this
docstring_tokens: Replaces the current data set by another .