Re: Did I find a (nearly-)gotcha here?

[Rod Kay <rodakay5@gmail.com>]

On 13/11/21 18:46, reinert wrote:
>
>     procedure test_a(ok :    out Boolean) is
>     begin
>        if false then
>           ok := true;
>        end if;
>     end test_a;
> 
> I get the following output (using GNAT Community Edition):
> 
> ok_a = FALSE
> ok_b = TRUE
> 
> As far as I understand, this is correct.
> However, I think I remember that (some) older versions of the GNAT compiler gave a different result. Could others try?  And does my program example reveal an unnecessary gotcha?
> 
> reinert
> 

Hi reinert,

    The value of an 'out' only parameter needs to be explicitly set. The 
initial value of the 'ok_a' variable will be discarded and then set to 
the value of the 'ok' parameter within 'test_a' when the call completes. 
Since 'ok' is not set in 'test_a' it's value is indeterminate (and 
therefore erroneous).

    I'd expect GNAT to issue a warning. Probably you need to add a flag 
to GNAT to enable that warning. Perhaps try adding '-gnatwa'.


Regards.