IteratorProtocol_Sequence_example.swift

import Foundation

class SomeClass {
    var someList = [1,2,3,4,5,6,7]
}

class SomeClassIterator: IteratorProtocol {
    private var someList: [Int]
    private var index: Int
    
    init(_ someList: [Int]) {
        self.someList = someList
        self.index = someList.startIndex
    }
    
    func next() -> Int? {
        if index < self.someList.endIndex {
            defer { index = self.someList.index(after: index) }
            return self.someList[index]
        } else {
            return nil
        }
    }
}

extension SomeClass: Sequence {
    func makeIterator() -> SomeClassIterator {
        return SomeClassIterator(self.someList)
    }
}

var someClassInstance = SomeClass()

for element in someClassInstance {
    print(element)
}