Collection.split(between:)

SplitBetween.swift

extension Collection {
    func split(between predicate: (Element, Element) throws -> Bool) rethrows -> [SubSequence] {
        guard !isEmpty else { return [] }

        var remainder = self[...]
        var slices: [SubSequence] = []

        for ((_, left), (index, right)) in indexed().pairs() {
            if try predicate(left, right) {
                slices.append(remainder.remove(upTo: index))
            }
        }

        slices.append(remainder)
        return slices
    }
}

extension Collection {
    func indexed() -> LazyMapCollection<Indices, (index: Index, element: Element)> {
        indices.lazy.map { ($0, self[$0]) }
    }
}

extension Sequence {
    func pairs() -> AnyIterator<(left: Element, right: Element)> {
        var iterator = makeIterator()
        var previous = iterator.next()

        return AnyIterator {
            guard let prev = previous,
                  let next = iterator.next()
            else { return nil }

            previous = next
            return (prev, next)
        }
    }
}

extension Collection where SubSequence == Self {
    mutating func remove(upTo index: Index) -> SubSequence {
        defer { self = self[index...] }
        return self[..<index]
    }
    
    mutating func remove(from index: Index) -> SubSequence {
        defer { self = self[..<index] }
        return self[index...]
    }
}

// usage:

print([1, 2, 3, 5, 6, 7, 10, 11].split(between: { $0 + 1 < $1 }))
// [ [1, 2, 3], [5, 6, 7], [10, 11] ]