each_cons from Ruby in Swift as a function on Sequence

Array+EachCons.swift

extension Collection {
    func eachConsecutive(_ size: Int) -> Array<SubSequence> {
        let droppedIndices = indices.dropFirst(size - 1)
        return zip(indices, droppedIndices)
            .map { return self[$0...$1] }
    }
}

Sequence+EachPair.swift

extension Sequence where SubSequence: Sequence, SubSequence.Iterator.Element == Iterator.Element {
    func eachPair() -> AnySequence<(Iterator.Element, Iterator.Element)> {
        return AnySequence(zip(self, self.dropFirst()))
    }
}