Re: In case statment? (was Re: is exception when others => null; smart?)

[Robert Spooner <rls19@psu.edu>]

If you avoid using "when others" and a value is added to the enumeration 
type later, the compiler will tell you where _all_ the case statements 
using that enumeration type are so that you can examine them and see 
what changes should be made.  Then you don't have to spend a lot of time 
using the debugger to crawl around in your code finding and fixing the 
parts that don't work right.  There's no guarantee that the default case 
will be correct for a new value, and shifting errors from run time to 
compile time is one of Ada's bigest advantages in my estimation.

Bob

Marin David Condic wrote:
> Well, one excuse for always having a "when others" in a case statement might
> be that you anticipate additions to the enumerated type driving it and you
> want the code to take come appropriate action if it gets a new, unknown
> value.
> 
> If you never use a "when others", you get the advantage that perhaps the
> compiler or runtime will catch inadvertent errors. If you always use "when
> others" you get the advantage of a built in accommodation for a software
> fault. Its an engineering tradeoff so "never" and "always" don't seem to
> really apply. It depends on the nature of the system and the consequences of
> hitting a case statement with a value not covered.

-- 
                             Robert L. Spooner
                      Registered Professional Engineer
                        Associate Research Engineer
                   Intelligent Control Systems Department

          Applied Research Laboratory        Phone: (814) 863-4120
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