OrderedDict.swift

public struct OrderedDict<K : Hashable, T> :
  CollectionType,
  DictionaryLiteralConvertible,
  CustomStringConvertible {
  
  private var keys: [K]
  private var vals: [K : T]

  public var endIndex: Int { return keys.endIndex }
  public var startIndex: Int { return 0 }
  
  public subscript (i: Int) -> (K, T) {
    get {
      return (keys[i], vals[keys[i]]!)
    } set(from) {
      self.vals[from.0] = from.1
      self.keys.append(from.0)
    }
  }
  
  public subscript (key: K) -> T? {
    get {
      return self.vals[key]
    } set(from) {
      self.vals[key] = from
      self.keys.append(key)
    }
  }
  
  public init(dictionaryLiteral elements: (K, T)...) {
    self.keys = elements.map { $0.0 }
    self.vals = Dictionary<K, T>()
    for (key, value) in elements { self.vals[key] = value }
  }
  
  public func generate() -> IndexingGenerator<Array<(K, T)>> {
    return self.keys.map { ($0, vals[$0]!) }.generate()
  }
  
  public var description: String {
    return ", ".join(self.keys.map {"[\($0):\(vals[$0]!)]"})
  }
}