Implementation of lazy collection in swift

Lazy collection implementation

typealias Closure = (Int) -> (Bool)

class MyFilterArrayView: SequenceType, GeneratorType {
  var _array: [Int]?
  var _lazyFilter: MyFilterArrayView?
  var _closure: Closure
  var _currentIndex: Int = 0
  
  var array: [Int] {
    get {
      var retArray = [Int]()
      _currentIndex = 0
      while let next = next() {
        retArray.append(next)
      }
      _currentIndex = 0
      
      return retArray
    }
  }
  
  init(arr: [Int], closure: Closure) {
    _array = arr
    _closure = closure
    _lazyFilter = nil
  }
  
  init(lazyFilter: MyFilterArrayView, arr: [Int], closure: (Int) -> Bool ) {
    _lazyFilter = lazyFilter
    _closure = closure
    _array = arr
  }
  
  func generate() -> MyFilterArrayView {
    return self
  }
  
  func filterItem(item: Int) -> Int? {
    if let lazyFilter = _lazyFilter {
      if lazyFilter.filterItem(item) == nil {
        return nil
      }
    }
    
    return _closure(item) ? item : nil
  }
  
  func next() -> Int? {
    
    for i in _currentIndex..<_array!.count {
      _currentIndex++
      
      if let filtered = filterItem(_array![i]) {
        return filtered
      }
    }
    
    return nil
  }
  
  func filter(closure: (Int) -> Bool) -> MyFilterArrayView {
    return MyFilterArrayView(lazyFilter: self, arr: _array!, closure: closure)
  }
}

struct MyLazyArray: SequenceType {
  var _array: [Int]
  
  init(_ arr: [Int]) {
    _array = arr
  }
  
  func generate() -> IndexingGenerator<[Int]> {
    return _array.generate()
  }
  
  func filter(closure: Closure) -> MyFilterArrayView {
    var w = _array
    return MyFilterArrayView(arr: _array, closure: closure)
  }
}

var testArray = [1,2,3,3,4,5]

func lazyNativeExample () {
  var lazyArray = lazy(testArray)
  var lazyFilter = lazyArray.filter{$0 > 2}.filter{$0 < 5}.filter{$0 < 4}
  
  var filteredArray = lazyFilter.array
  println(filteredArray)
  
  for item in lazyFilter {
    println(item)
  }
}

func lazyCustomExample () {
  var lazyArray = MyLazyArray(testArray)
  
  var lazyFilter = lazyArray.filter{$0 > 2}.filter{$0 < 5}.filter{$0 < 4}
  
  var filteredArray = lazyFilter.array
  println(filteredArray)
  
  for item in lazyFilter {
    println(item)
  }
}

lazyNativeExample()
lazyCustomExample()