Re: Gnat 2013 is out!

[Adam Beneschan <adam@irvine.com>]

On Thursday, May 30, 2013 3:39:46 AM UTC-7, Simon Wright wrote:

> If I read the RM right (I probably don't), then because in this case I
> don't read the values assigned (they are dummies, after all) I should be
> OK. (ARM 6.2 (12/3)).

They may be dummies from the caller's point of view, but I'm concerned about the callee's.  The callee doesn't know that it's going to get passed "dummy" variables.  If it reads its own OUT parameters after it sets them, then there could be aliasing problems.

If the callee is a subprogram in a different package, then you really shouldn't assume anything about what's in the body of the callee, other than what's in the "contract" (whether the contract is expressed as Ada preconditions or just comments).  To me, this means that if the contract doesn't say it's OK for the parameters to overlap, then you should assume that the callee *could* do something that will go wrong if the parameters overlap.  However, if this is your own subprogram in your own package body calling another subprogram in the same package body, it's more acceptable (IMHO) to assume that overlapping is OK.

                         -- Adam