骨が出来た #CodePiece

CodePiece.swift

struct JoinedCollection<C1: Collection, C2: Collection, Element>: Collection
where C1.Element == Element, C2.Element == Element, C1.Index == Int, C2.Index == Int {
  var left: C1
  var right: C2

  init(_ left: C1, _ right: C2) {
    self.left = left
    self.right = right
  }

  /// Sequence
  struct Iterator: IteratorProtocol {
    var iter1: C1.Iterator
    var iter2: C2.Iterator

    init(_ c: JoinedCollection) {
      self.iter1 = c.left.makeIterator()
      self.iter2 = c.right.makeIterator()
    }

    mutating func next() -> Element? {
      if let e = iter1.next() {
        return e
      }
      return iter2.next()
    }
  }

  func makeIterator() -> Iterator {
    return Iterator(self)
  }

  /// Collection
  var startIndex: Int {
    left.startIndex
  }
  var endIndex: Int {
    left.endIndex + right.endIndex
  }

  func index(after i: Int) -> Int {
    i + 1
  }

  subscript(_ i: Int) -> Element {
    if i < left.endIndex {
      return left[i]
    }
    return right[i - left.endIndex]
  }
}

extension JoinedCollection: BidirectionalCollection
where C1: BidirectionalCollection, C2: BidirectionalCollection {
  func index(before i: Int) -> Int {
    i - 1
  }
}

extension JoinedCollection: RandomAccessCollection
where C1: RandomAccessCollection, C2: RandomAccessCollection {}


extension JoinedCollection {
  init<C3, C4>(_ c1: C1, _ c3: C3, _ c4: C4)
  where C2 == JoinedCollection<C3, C4, Element> {
    self.left = c1
    self.right = .init(c3, c4)
  }

  init<C3, C4, C5, C6>(_ c3: C3, _ c4: C4, _ c5: C5, _ c6: C6)
  where C1 == JoinedCollection<C3, C4, Element>, C2 == JoinedCollection<C5, C6, Element> {
    self.left = .init(c3, c4)
    self.right = .init(c5, c6)
  }
}

let j01 = JoinedCollection([], [3, 4, 5])
print(j01)

print("\nCount: ", j01.count)

print("\nElements:")
j01.forEach { print($0) }

print("\nIndex Access:", j01[2])

print("\nReserved:")
j01.reversed().forEach { print($0) }

let j02 = JoinedCollection([0, 1, 2], [10, 11, 12, 13], [20, 21, 22, 23, 24])
print(j02)

print("\nCount: ", j02.count)

print("\nElements:")
j02.forEach { print($0) }

print("\nIndex Access:", j02[2], j02[4], j02[8])

print("\nReserved:")
j02.reversed().forEach { print($0) }