Re: Passing the same actual as both in and out formal parameters?

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

Jean-Pierre Rosen wrote on comp.lang.ada:
> Ludovic Brenta a écrit :
>
>  procedure P (A : in T; B : out T) is
>> begin
>>    B.L := A.M; -- does this change A.L too?
> Yes
>>    B.M := A.L; -- bug: A.L has been clobbered, now B.M = B.L?
>> end P;
>
>> My concern stems from the fact that T is tagged (I cannot change
>> that), so Object is passed by reference as both A and B.
>
>> Am I right to be concerned?
>
> Depend on what your concern is ;-)
> The semantic is well defined: tagged types are by-reference type. If you
> want to swap two fields of different parameters of the same type, use a
> local variable.

My exampled was heavily simplified; the actual type has about a
hundred components and the procedure P is a little more complex than
swapping components :)

But thanks for the responses, Niklas and Jean-Pierre. They confirm my
suspicion.

--
Ludovic Brenta.