Is it possible to create a cartesian product function with parameter packs?

[Danny]

This type of combination/permutation is missing. What is it called?

Here's a parameter pack implementation I cooked up: struct Product<each C: Collection>: IteratorProtocol, Sequence { var collection: (repeat each C) var index: (repeat (each C).Index) var done: Bool init(_ collection: repeat each C) { self.collection = (repeat each collection) self.index = (repeat (each collection).startIndex) self.done = false // We're immediately done if any collection is empty. for (c, i) in repeat (each collection, each index) { if (i ==…