Re: RISC

["Marin David Condic" <marin.condic.auntie.spam@pacemicro.com>]

No question is stupid if you don't know the answer.

There is no reason you *can't* raise an exception in a function. ("Throw" is
the C++ terminology - "Raise" is the Ada terminology) There are conditions
under which a function will generate an exception on its own even if you
don't explicitly raise one. (Example: Hit the end of a function without
returning a result. This will raise "Program_Error" - if I remember
correctly.)

The question "Is it good practice to raise exceptions in functions?" is
fair. The answer is: "It Depends..." If you encounter a condition that is
truly "exceptional" and/or it represents some sort of erroneous condition,
then raising an exception is fair to do. Example: You write a function for
which some combination of parameters makes no sense or leaves the function
undefined. Go ahead and raise an exception. If you encounter some sort of
normal, expected condition and use an exception for some sort of transfer of
control, this is generally considered impolite and/or bad form. Example: You
design a function to raise an exception to accomplish a loop exit when you
hit the terminal condition for the loop.

When to raise an exception will also depend on the nature of your system. If
the system encounters an error is it proper for the program to stop running?
If not, then you may not want to raise the exception - or at least guarantee
you have a handler for all exceptions. Again, "It Depends."

Its hard to come up with absolute rules since it often requires subjective,
artistic judgements. Just keep in mind that the intention is to have a
mechanism that deals with *errors* - not anticipated conditions that can be
accommodated with some sort of "normal" processing.

MDC

--
Marin David Condic
Senior Software Engineer
Pace Micro Technology Americas    www.pacemicro.com
Enabling the digital revolution
e-Mail:    marin.condic@pacemicro.com
Web:      http://www.mcondic.com/


"chris.danx" <chris.danx@ntlworld.com> wrote in message
news:Cous6.1406$lC5.401322@news2-win.server.ntlworld.com...
> Maybe i'm being stupid, please feel free to inform me if this is so, but
> i'll ask anyway.
>
> I know functions are allowed to throw exceptions in Ada.  What i want to
> know is acceptable practice?  I use exceptions with procedures, no
problem,
> but someone -- can't remember who exactly, it was ages ago -- suggested
it's
> bad practice!  What do you think?  If i remember correctly i think this
> related to C++, or something, so maybe it's irrelevant to Ada.
>
> Just curious,
> Chris Campbell
>
>