Itertools

[ichthyo]

Start a collection of Iterator-tools, similar to the Python module, or the Commons-Collections IteratorUtils, or the respective features of Groovy.

Of course we're not writing a library, so we'll add here what is needed, starting with

• a filtered iterator
• a transform iterator

Possibly also (if not too difficult to implement)

• a chain iterator
• a dropwhile

[ichthyo]

did the first steps here, due to the ContentsQuery, which can be implemented quite elegantly with a filter on top of the scope enumeration capability of the PlacementIndex

[ichthyo]

implemented an transform iterator, allowing to define PlacementIndex::iterator in terms of an transformer and a range yielded from the embedded hashtable

[ichthyo]

added caching to FilterIter, implemented duplicate-filtering iterator

[ichthyo]

(In #486) ugly, but not an urgent problem right now. Pushing to future

[ichthyo]

The basics are implemented and have proven to be very helpful already. Leaving the extensions to be done on demand.