Re: Limited_Controlled types as 'out' arguments

[Vinzent Hoefler <ada.rocks@jlfencey.com>]

Lutz Donnerhacke wrote:

>* Dmitry A Kazakov wrote:
>
[reading "out"-Parameters]
>> You can in Ada 95.
>
>Oops. Why?

Convinience. Sometimes it avoids the temporary copy that would be
needed in Ada83. See the example below.

>This is a clear data flow error,

Not if you have updated the object inside the procedure before reading
it, consider this:

|   procedure Set_Timer_Limits (Input_Frequency : in Frequency;
|                               Limit           : in Min_Max;
|                               Timer           : out TxParm;
|                               In_Range        : out Boolean) is
|   begin
|      --  here the Timer object is not yet initialized, reading
|      --  would be a data flow error
|      Timer.Min := Clamp8254 (Input_Frequency / Limit.Max);
|      Timer.Max := Clamp8254 (Input_Frequency / Limit.Min);
|
|      --  but here we can simply read it without data flow error
|      --  or the need for a temporary copy
|      In_Range := ((Input_Frequency / Timer.Max) > Limit.Min) and
|                  ((Input_Frequency / Timer.Min) < Limit.Max);
|   end Set_Timer_Limits;


Vinzent.