Re: Printing Enum Variable Re: Linux World

[Ehud Lamm <mslamm@mscc.huji.ac.il>]

On Thu, 4 Mar 1999 robert_dewar@my-dejanews.com wrote:

>  Enumeration
> types are an important abstraction, and their absence
> from C is a significant missing capability.
> 
> Calling something an enum does not make it an enumeration
> type!
> 

Time and again I am amazed how this simple festure ofthe language stumps
people. I see exercises which show understanding of important and
difficult concepts like genericity - but fail to exploit enumeration type
where appropriate. This should really end up on my idiom list. 

Just as the ultimate simple exmaple, for lurkers who are studying the
language, consider that when you have a situation where you know exactly
the class of possible values enumeration types allow you to (1) name them
and (2) implicitly assume that the value is valid, without having to check
it each time it is used. Example:
If I have a function that receives a coind value, which must be a quarter
or a cent, I can coide it like this:
type coin is (quarter,cent)
...
case Coin_val is
when quarter =>
when cent =>
end case

where as a lower level of abstractenss and more work is needed when you
define coin to a integer type:
case Coin_val is
when 1 =>
when 25=>
when others => raise Coin_Error;
end case

(This is a nice situation, because many people want to declare an integer
subtype with two, non-consecutive values).

Ehud Lamm     mslamm@pluto.mscc.huji.ac.il
http://www2.cybercities.com/e/ehud