FYI, there’s an updated discussion since the first link (only 6 months old, so relatively recent), with a prototype implementation: [Prototype] Protocol-powered generic trimming, searching, splitting,
It’s a good time to think about this. We recently added RangeSet and DiscontiguousSlice, and I think that might have reignited interest in predicate-matching (perhaps something like this pitch). If we can come up with a cohesive design for all of this, we should have a solid foundation for one-off patterns via regex literals.