Explore Swift Challenge #2

TakeWhile.swift

struct TakeWhile<S: SequenceType>: SequenceType {
  private let seq: S
  private let block: (S.Generator.Element) -> Bool
  init(_ seq: S, block: (S.Generator.Element) -> Bool) {
    self.seq = seq
    self.block = block
  }
  func generate() -> GeneratorOf<S.Generator.Element> {
    var gen = seq.generate()
    return GeneratorOf<S.Generator.Element> {
      if let element = gen.next() {
        if self.block(element) {
          return element
        }
      }
      return nil
    }
  }
}

Array(TakeWhile(["a", "a", "a", "b", "c"]) { $0 == "a" })