Concept "lumiera forward iterator"

[Ichthyostega]

Over time, various ad-hoc definitions for iteration were utilised in the code base, especially in Steam-Layer. While typicaly somehow modeled after the iterators in the C++ STL, these can not be combined and each one has its specific twists. A common concept should thus be factored out from the actual usages and applied uniformly, going forward. An iterator should be easy to understand, and usable in for-each loops. Document the new specification by Unit test and write a DesignProcess entry.

Explanation: The STL defines various, intricately layered iterator concepts. Ichthyo considers most of these capabilities to be excessive and geared more towards the implementation of algorithms than serving as a means of abstraction. In contrast, many modern programming languages rely on a radically simple iterator concept that allows one to pull a sequence of values – and nothing more. Providing only such an iterator often leads to clearer APIs.

Thus the idea is to formulate a concept in that is roughly in compliance with STL's input / forward iterator -- but augmented by an stop-iteration test. Obviously, there should be some easy-to-use support templates to help building compliant iterators. This would give us basic STL integration and look familiar to C++ and Java programmers without compromising the clean APIs.

[Ichthyostega]

doing some initial steps here, because I need to write yet more iterators...

probably this will stay unfinished for some time to come, because I've more urgent other work...

[Ichthyostega]

I've now implemented 3 basic templates, which should be enough for now to define the Session interface.

TODO: retrofit the existing iterators, more unit test coverage with real-world use cases, document the iterator concept

[Ichthyostega]

...so, what remains here to do?

• write a Design-Process entry to document the concept.
• have a look at existing iterators, which could be retrofitted easily
• create tickets for the remaining iterators, to be cleaned up later

The summary of the concept, as it's implemented now, can be found in the doxygen of lib/iter-adapter.hpp

[Ichthyostega]

Successfully used now within QueryResolver. Cleaned up the back-link in IterAdapter. Wrote a documentation Page to the TiddlyWiki and also used the same text as ​DesignProcess-Entry

[Undercover Agent]

Migration MasterTickets ⟼ Subtickets-plugin

[Ichthyostega]

Has become a core element of Lumiera

Many years later, this Forward Iterator Concept evolved into a cornerstone and defining element in the codebase. It has proven to be flexible, robust and easy to implement — and gave rise to various elaborate functional evaluation patterns. Notably the IterExplorer allows to build processing pipelines, optionally with dynamic tree expansion and depth-first search.