Mapping over the range and pattern matching operators
30 Jan 2021 ⇐ Notes archive(This is an entry in my technical notebook. There will likely be typos, mistakes, or wider logical leaps — the intent here is to “let others look over my shoulder while I figure things out.”)
Two tricks for the operator and pointfreeleaning crowd:

To quickly form ranges from a sequence of
indices
, you can usezip(indices, indices.dropFirst()).map(..<)
(or subbing in the closed range operator — the onesided variants are ambiguous in the pointfree style)^{1}.let odds = [1, 3, 5, 7] zip(odds, odds.dropFirst()).map(..<) // ⇒ [(1..<3), (3..<5), (5..<7)]

And tangentially, to test if parallel sequences of ranges and values match against one another.
// (…continuing from above.) let odds = [1, 3, 5, 7] let oddRanges = zip(odds, odds.dropFirst()).map(..<) let evens = [2, 4, 6] zip(oddRanges, evens).map(~=) // ⇒ [true, true, true]

Ended up using this in a note on
Collection.batchedSubscribe(by:)
. ↩