Trying to get generic code from working Iterator pattern

Here is the code that works fine and this is implementation of the Iterator pattern:

struct Candies {
    let candies: [String]
}

extension Candies: Sequence {
    func makeIterator() -> CandiesIterator {
        return CandiesIterator(sequence: candies, current: 0)
    }
}

struct CandiesIterator: IteratorProtocol {

    let sequence: [String]
    var current = 0

    mutating func next() -> String? {
        defer { current += 1 }
        return sequence.count > current ? sequence[current] : nil
    }
}

Here is the code that I thought to be as a generic variation of the code above but I have two errors (see below the code):

struct Whatevers<T> {
    let whatevers: [T]
}

extension Whatevers: Sequence {
    func makeIterator() -> Whatevers<T>.Iterator {
        return WhateversIterator(sequence: whatevers, current: 0)
    }
}


struct WhateversIterator<T>: IteratorProtocol {
    let sequence: [T]
    var current = 0

    mutating func next() -> WhateversIterator.Element? {
        defer { current += 1 }
        return sequence.count > current ? sequence[current] : nil
    }
}

error: MyPlayground.playground:854:1: error: type 'Whatevers' does not conform to protocol 'Sequence' extension Whatevers: Sequence { ^

error: MyPlayground.playground:861:8: error: type 'WhateversIterator' does not conform to protocol 'IteratorProtocol' struct WhateversIterator: IteratorProtocol {

Can someone explain what is incorrect in this code. And how can I make it work?