public void filter_and_map_in_place (CapsFilterMapFunc func)
Calls the provided function once for each structure and caps feature in the Caps.
In contrast to @foreach, the function may modify the structure and
features. In contrast to filter_and_map_in_place, the structure and features are removed from the caps if
false is returned from the function. The caps must be mutable.
a function to call for each field