In order to increase usability of API, Qt needs to use ranges.

What is "ranges"?
This is a modern way to deal with collections of elements that allows making operations composable and perform lazy evaluation.

Why?

1. Modern
2. Lazy
3. Clean code
4. Clean interfaces
5. Functional
6. Composable

Proof of concept?
Using ranges (+optionally coroutines) for traversing QObject tree: https://git.qt.io/vifanask/qobject-with-ranges

When?
C++20 so far.

Anything to play with?
https://github.com/ericniebler/range-v3 (Fully compatible with C++17; boost license)

Note: subtasks will be added if we decide to proceed with this research.