/**
* @param callable $fnValueMap($value, $key) -- function that returns the new value.
* @param callable $fnKeyMap($key, $value) [optional] -- function that returns the new key
* @return static
*/
public function map($fnValueMap, $fnKeyMap = null)
{
return static::make(IterationTraits::map($this, $fnValueMap, $fnKeyMap));
}
