extension Dictionary {
 
 public func map<T: Hashable, U>(transform: (Key, Value) -> (T, U)) -> [T: U] {
   var result: [T: U] = [:]
   for (key, value) in self {
     let (transformedKey, transformedValue) = transform(key, value)
     result[transformedKey] = transformedValue
   }
   return result
 }
 
 public func map<T: Hashable, U>(transform: (Key, Value) throws -> (T, U)) rethrows -> [T: U] {
   var result: [T: U] = [:]
   for (key, value) in self {
     let (transformedKey, transformedValue) = try transform(key, value)
     result[transformedKey] = transformedValue
   }
   return result
 }
}