Re: Exceptions

[Maciej Sobczak <see.my.homepage@gmail.com>]

On 13 Gru, 14:40, Robert A Duff <bobd...@shell01.TheWorld.com> wrote:

> The solution to "when others => null;" and the like is better
> education.

Isn't it also a solution for all the presumed problems of C/C++?
Sorry, could not resist. ;-)

> I don't consider Constraint_Error "mere", by the way.
> It almost always represents a bug.

What about a situation when a user entered an input data that was
outside of legal (and documented) range? Or that caused our of range
value further down the pipe?
This is not necessarily a bug, just an indication that the value is
out of range. The exception can help to come back to the input loop
and repeat the user scenario, abandoning all the state that was
created in the meanime. This way the program does not enter into any
abnormal state.

> > Why not terminating the program right on the spot by simply:
>
> > pragma Assert (False);

> That doesn't terminate the program on the spot.
> It raises Assertion_Failure.

Right. I was somehow convinced that Assert has this magic property of
switching the world off, like the assert macro in C and C++.

> I consider all of these:
>
>     pragma Assert (False);
>     Assert (False); -- Assert is a user-defined procedure
>     raise Program_Error;
>     raise Bug; -- Bug is a user-defined exception used project-wide
>
> to be legitimate ways of reporting a self-detected bug.

OK, this sounds reasonable.

> There ought to be a standard predefined procedure for stopping the
> program "on the spot".  Since there isn't, you can import "exit".

I was wandering whether there is any standard mechanism for this.

--
Maciej Sobczak * www.msobczak.com * www.inspirel.com