message: added ObjectKeys type helper function
diff: @@ -20,3 +20,7 @@ export type ArrayCtor<T> = { new(size: number): { [i: number]: T, length: number
  export type AssignableArrayLike<T> = { [i: number]: T, length: number }
  export type NonNullableArray<T extends any[] | ReadonlyArray<any>> = T extends any[] ? NonNullable<T[0]>[] : ReadonlyArray<NonNullable<T[0]>>
  +
  +export function ObjectKeys<T extends object>(o: T) {
  + return Object.keys(o) as (keyof T)[]
  +}
  \ No newline at end of file
  