# Type.KeyOf

Extracts Keys from an Object or Tuple.

## Example

Example usage is shown below.

    const T = Type.Object({
      x: Type.Number(),
      y: Type.Number(),
      z: Type.Number()
    })

    const S = Type.KeyOf(T)                             // const S: TUnion<[
                                                        //  TLiteral<'x'>,
                                                        //  TLiteral<'y'>,
                                                        //  TLiteral<'z'>
                                                        // ]>