Iterator

import Utils

struct CircularArray<T>

init(capacity: Int)

let capacity: Int

var count: Int { get }

var isEmpty: Bool { get }

subscript(index: Int) -> T { get set }

func makeIterator() -> Iterator

mutating func push(_ value: T)

protocol IteratorProtocol<Element>

A type that supplies the values of a sequence one at a time.

init(values: [T], capacity: Int, insertPos: Int)

mutating func next() -> T?