Potentially stupid newbie question

[Nick Sabalausky]

"Mr. Red" <garfieldrules at sbcglobal.net> wrote in message 
news:g6vv1i$1nu1$1 at digitalmars.com...
>I had been referring to when the methods were exclusive to the derived 
>class, but considering that in my would-be program the derived classes 
>mostly just redefine functions already present in the base class, the first 
>method is better.  I was just whipping up a quick test program with an 
>unsophisticated hierarchy and didn't think to include the base class's 
>version of the function too.  Thank you for your help!

If you have an array of a base type (like Cat), it doesn't usually make much 
sense to try to access things that only exist in a derived type. This is 
because, for instance, you can be absolutely certain that "cat[someIndex]" 
is going to be a Cat, but you have no idea if it's also a Tiger or a Lion or 
whatever. So "someCat.doSomethingOnlyALionCanDo()" is risky business, 
because what if "someCat" isn't a Lion? Just because you put a Lion into 
myCat earlier in the program doesn't mean that later parts can be certain 
that that happened and is still true.

Once in a while you will see cases where it's useful to say something like 
"Is this cat a Lion? If it's a Lion, do this special Lion-only thing on it". 
Polymorphism (ie: Steven's first part) is the usual/preferred way to handle 
this, when possible. But once in a while you might come across cases where 
that approach just isn't very applicable. In those cases, you can do RTTI 
(Run-Time Type Identification, ie, Steven's second part).