mixins.scala

abstract class AbsIterator {
	type T
	def hasNext: Boolean
	def next: T
}

trait RichIterator extends AbsIterator {
	def foreach(f: T => Unit) { while (hasNext) f(next) }
}

class StringIterator(s: String) extends AbsIterator {
	type T = Char
	private var i = 0
	def hasNext = i < s.length()
        def next = { val ch = s charAt i; i += 1; ch }
}

object Main extends App {
	class Iter extends StringIterator("This in swift when?") with RichIterator
	val iter = new Iter
	iter foreach println
}

swiftattempt.swift

protocol AbsIterator {
    typealias T
    var hasNext: Bool {get}
    func next() -> T
}

protocol RichItarator: AbsIterator {
    func forEach(f: T -> Void)
}

extension RichItarator {
    func forEach(f: T -> Void) {
        while hasNext {
            f(next())
        }
    }
}

class StringIterator: AbsIterator {
    let string: String
    typealias T = Character
    var i = 0
    
    var hasNext: Bool {
        return i < string.characters.count
    }
    
    func next() -> T {
        return string[string.startIndex.advancedBy(i)]
    }
    
    init(string: String) {
        self.string = string
    }
}

extension StringIterator: RichItarator {}