But function toStartOfWeek is always monotonic and it's better to keep this behaviour.

The same about toYearWeek.

This looks wrong, because, it will erroneously return true for ranges, that start at the same week, but last more than year and will return false for ranges, that are in one year, but start at different weeks. I think, it's better to use ToStartOfYearImpl as FactorTransform for toWeek like it is done, e.g. for function toMonth in DateTimeTransforms.h.

Yeah. I didn't understand the code style. It should be trivial :) Updated

ToStartOfYearImpl? We need to check, that two dates belong to the same year.

but toStartOfWeek contains year

┌─toStartOfWeek(now())─┐
│           2021-05-23 │
└──────────────────────┘

Yes, but toWeek in range of one year can be treated as monotonic, but toStartOfWeek doesn't allow this.

Ah, right. I failed to understand it twice somehow ...