original_string: function map (callable $fn, $arg = null)
    {
      $this->setIterator (new MapIterator ($this->getIterator (), $fn, $arg));
      return $this;
    }
code: function map (callable $fn, $arg = null)
    {
      $this->setIterator (new MapIterator ($this->getIterator (), $fn, $arg));
      return $this;
    }
code_tokens: function map ( callable $ fn , $ arg = null ) { $ this -> setIterator ( new MapIterator ( $ this -> getIterator ( ) , $ fn , $ arg ) ) ; return $ this ; }
docstring: Transforms the iterated data using a callback function.
  
  @param callable $fn  A callback that receives a value, a key and an option extra argument, and returns the new
  value.<br> It can also receive the key by reference and change it.
  <p>Ex:<code>  ->map (function ($v, &$k) { $k = $k * 10; return $v * 100; })</code>
  @param mixed    $arg An optional extra argument to be passed to the callback on every iteration.
  <p>The callback can change the argument if it declares the parameter as a reference.
  @return $this
docstring_tokens: Transforms the iterated data using a callback function .