Some generics stuff

/// [1, 2, 3, 4, 5] -> [[1,2], [2,3], [3,4], [4,5]]

public func makeClosePairs<C: Collection>(c: C) -> [C.SubSequence] {

    var out: [C.SubSequence] = []

    var index = c.startIndex
    while index < c.endIndex {
        let first = index
        let second = c.index(after: first)
        guard second < c.endIndex else { break }
        let slice = c[first...second]
        out.append(slice)
        index = second
    }

    return out

}

/// [1, 2, 3, 4, 5, 6] -> [1, 2, 3] [4, 5, 6]

func sliceOnTwo<D: Collection>(collection: D) -> (left: D.SubSequence, right: D.SubSequence)
    where D.Index: Strideable, D.Index.Stride: SignedInteger
{
    let distance = collection.startIndex.distance(to: collection.endIndex)
    let middlecount = distance / 2
    let middle = collection.startIndex.advanced(by: middlecount)
    let firsthalf = collection[...middle]
    let secondhalf = collection[middle...]
    return (left: firsthalf, right: secondhalf)
}