ZipExtended2

zipextended2.swift

struct ZipExtendGenerator2<E0 : GeneratorType, E1 : GeneratorType> : GeneratorType {
  typealias Element = (E0.Element?, E1.Element?)

  var e0: E0
  var e1: E1

  init(_ e0: E0, _ e1: E1) {
    self.e0 = e0
    self.e1 = e1
  }

  mutating func next() -> Element? {
    let first = e0.next()
    let second = e1.next()

    if first == nil && second == nil {
      return nil
    }

    return (first, second)
  }
}

struct ZipExtend2<S0 : SequenceType, S1 : SequenceType> : SequenceType {
  typealias Stream1 = S0.Generator
  typealias Stream2 = S1.Generator
  typealias Generator = ZipExtendGenerator2<S0.Generator, S1.Generator>

  let s0: S0
  let s1: S1
  
  init(_ s0: S0, _ s1: S1) {
    self.s0 = s0
    self.s1 = s1
  }
  func generate() -> Generator {
    return ZipExtendGenerator2(self.s0.generate(), self.s1.generate())
  }
}