Iterating all possible combinations of r elements in a given array of objects in Swift

Combinator.swift

class Combinator<Object>: IteratorProtocol {
    typealias Element = [Object]
    var objects: [Object]
    var numberOfSelection: Int

    private var currentIndexes: [Int]
    private var done = false

    func next() -> [Object]? {
        guard !currentIndexes.isEmpty else { return nil }
        guard objects.count > numberOfSelection else {
            currentIndexes.removeAll()
            return objects
        }

        guard currentIndexes.last != nil, currentIndexes.last! >= objects.endIndex else {
            return currentObjectsAndIncreaseIndex()
        }

        currentIndexes.popLast()
        increaseLastIndex()
        while let last = currentIndexes.last, last >= objects.endIndex - (numberOfSelection - currentIndexes.count) {
            currentIndexes.popLast()
            increaseLastIndex()
        }

        guard !currentIndexes.isEmpty else { return nil }

        while currentIndexes.count < numberOfSelection {
            currentIndexes.append((currentIndexes.last ?? -1) + 1)
        }

        return currentObjectsAndIncreaseIndex()
    }

    private func currentObjectsAndIncreaseIndex() -> [Object] {
        let objs = currentIndexes.map { objects[$0] }
        increaseLastIndex()
        return objs
    }

    private func increaseLastIndex() {
        guard currentIndexes.count > 0 else { return }
        currentIndexes[currentIndexes.endIndex - 1] += 1
    }

    init(_ objects: [Object], _ numberOfSelection: Int) {
        self.objects = objects
        self.numberOfSelection = numberOfSelection

        guard numberOfSelection > 0, !objects.isEmpty else {
            currentIndexes = []
            return
        }

        currentIndexes = Array(0..<numberOfSelection)
    }
}

Test.swift

let c = Combinator(["A", "K", "Q", "J", "T", "9", "8"], 5)
while let i = c.next() {
    print("\(i)")
}
/*
Print Result:
["A", "K", "Q", "J", "T"]
["A", "K", "Q", "J", "9"]
["A", "K", "Q", "J", "8"]
["A", "K", "Q", "T", "9"]
["A", "K", "Q", "T", "8"]
["A", "K", "Q", "9", "8"]
["A", "K", "J", "T", "9"]
["A", "K", "J", "T", "8"]
["A", "K", "J", "9", "8"]
["A", "K", "T", "9", "8"]
["A", "Q", "J", "T", "9"]
["A", "Q", "J", "T", "8"]
["A", "Q", "J", "9", "8"]
["A", "Q", "T", "9", "8"]
["A", "J", "T", "9", "8"]
["K", "Q", "J", "T", "9"]
["K", "Q", "J", "T", "8"]
["K", "Q", "J", "9", "8"]
["K", "Q", "T", "9", "8"]
["K", "J", "T", "9", "8"]
["Q", "J", "T", "9", "8"]
*/