CustomArray

CustomArray.swift

import Foundation

struct CustomArray<Element>: MutableCollection, RangeReplaceableCollection, RandomAccessCollection {

  typealias Index = Int
  typealias SubSequence = CustomArray<Element>

  private var storage = NSMutableArray()

  var startIndex: Int {
    return 0
  }

  var endIndex: Int {
    return storage.count
  }

  private mutating func copyBufferIfNeeded() {
    guard !isKnownUniquelyReferenced(&storage) else { return }
    storage = storage.mutableCopy() as! NSMutableArray
  }

  subscript(position: Int) -> Element {
    get {
      return storage.object(at: position) as! Element
    }
    mutating set(newValue) {
      copyBufferIfNeeded()

      if storage.count == position {
        storage.add(newValue)
      } else {
        storage.replaceObject(at: position, with: newValue)
      }
    }
  }

  subscript(bounds: Range<Index>) -> SubSequence {
    get {
      return CustomArray<Element>(storage.objects(at: IndexSet(integersIn: bounds)) as! [Element])
    }
    set {
      copyBufferIfNeeded()

      let range = NSRange(bounds)

      storage.replaceObjects(in: range, withObjectsFrom: Array(newValue))
    }
  }

  mutating func replaceSubrange<C, R>(_ subrange: R, with newElements: C) where C : Collection, R : RangeExpression, Element == C.Element, CustomArray<Element>.Index == R.Bound {
    copyBufferIfNeeded()

    let range = NSRange(subrange)
    storage.replaceObjects(in: range, withObjectsFrom: Array(newElements))
  }
}