Learning Swift sequence protocols

fibonacci.swift

struct FibIterator: IteratorProtocol {
    var currentCount = 0
    var maxCount: Int?
    var maxValue: Int?
    var currentFib: Int
    var previousFib: Int
    mutating func next() -> Int? {
        if let maxCount = maxCount, currentCount >= maxCount {
            return nil
        }
        let next = currentFib + previousFib
        if let maxValue = maxValue, next > maxValue {
            return nil
        }
        previousFib = currentFib
        currentFib = next
        currentCount += 1
        return next
    }
    init(current: Int = 1, previous: Int = 0, count: Int? = nil, max: Int? = nil) {
        currentFib = current
        previousFib = previous
        maxCount = count
        maxValue = max
    }
}


struct FibSequence: Sequence {
    let max: Int?
    let count: Int?
    func makeIterator() -> FibIterator {
        return FibIterator(count: count, max: max)
    }
    init(count: Int? = nil, max: Int? = nil) {
        self.max = max
        self.count = count
    }
}

// Simple
var last = 0
var current = 1

let fibIter = AnyIterator<Int> {
    defer {
        var next = last + current
        last = current
        current = next
    }
    return last
}

let fibSeq = IteratorSequence(fi)
Array(fibSeq.prefix(10))