   end
 
   @doc """
-  Calculates the difference between two dates,
-  in a full number of days, returning `{:ok, difference}`.
-
-  Note that only `Date` structs that follow the same or
-  compatible calendars can be compared this way.
-  If two calendars are not compatible,
-  `{:error, :incompatible_calendars}` is returned.
+  Calculates the difference between two dates, in a full number of days.
+
+  Note that only `Date` structs that follow the same or compatible
+  calendars can be compared this way. If two calendars are not compatible,
+  it will raise.
 
   ## Examples
 


  @doc """
  Returns the difference between two `Time` structs.
  """
  @spec diff(Time.t, Time.t, System.time_unit) :: integer
  def diff(%Time{} = time1, %Time{} = time2, unit \\ :second) do

  end

  @doc """
  Subtracts `datetime2` from `datetime1`.

  The answer can be returned in any `unit` available from `t:System.time_unit/0`.

  This function returns the difference in seconds where seconds are measured
  according to `Calendar.ISO`.

  ## Examples

