[hakunin]

Lazy enumeration can also save memory, because you aren’t storing entire collections during intermediate steps, and it works with infinite/unknown size collections. Such as streaming data.

Some examples:

I wrote a utility gem a while ago that lets you lazily intersect, union, etc various potentially infinite streams of data. https://github.com/maxim/enum_utils/

I also used lazy enumeration for traversing the wordmap in my no-RAM static storage gem. https://github.com/maxim/wordmap/

[hansvm]

In the worst case, that must have intermediate space requirements equal to the entire collections, right?

[hakunin]

I don’t think that can happen because all those functions assume the streams are consistently sorted.

[hansvm]

Ohhhhh, nice. Yeah, sorted data is powerful. Thanks for pointing that out.

[pyinstallwoes]

How is it different than a window, rolling window?

[hakunin]

It's probably a version of that. But since data is assumed sorted, memory requirements almost never grow beyond one item per stream.