🚀 go-pugleaf

orpheus@reed.edu (P. Hawthorne) writes:
>It seems un-structured. What would Djikstra say?

I find myself using member() in the TCL for three chief purposes:

1]  ASSERTs.  It's handy to make sure something is what you expect.
2]  In CCollaborators' ProviderChanged() method, testing whether the
provider that changed is of a certain type.  (For non-TCLers,
CCollaborator is a class whose instances can DependUpon() each other;
whenever a CCollaborator calls BroadcastChange(), all itsDependents
get their ProviderChanged() method called.  Very handy, but to design a
flexible system, a CCollaborator has to expect to get lots of unwanted
ProviderChanged() messages.)
3]  In methods that, I suspect, would be called "friend" under C++.
Think C doesn't give you a way to link a bunch of classes together and
say "only these classes are friends of mine, and only my friends can
call the following methods."  (Is that essentially what C++ does?)
So you have to fake it with run-time checking on your own.

>When I use it...I worry that perhaps a seriously
>abstract class variable could formalize whatever notions are at work. Or I
>think that it is a kludge so that I can put off a total overhaul until I
>figure out how to work in the exceptional classes.

If you write, for example,

void CEatingObject::eatObject(CFoodObject *theFoodObj)
{
	if (member(theFoodObj, CBanana)) gobbleBanana();
	else if (member(theFoodObj, CCookie)) munchCookie();
	else if (member(theFoodObj, CSquid)) slurpSquid();
}

...then you're misusing member().  (In this case, the eating method
should go into CFoodObject, not CEatingObject, and should be overridden
by all those subclasses.)

If Think C's lack of multiple inheritence forces you to construct a dual
class hierarchy, I can see having to misuse member(), as a consequence.

But otherwise, unless you're doing something like CEatingObject, I
wouldn't worry about it.
-- 
 Jamie McCarthy      Internet: k044477@kzoo.edu      AppleLink: j.mccarthy
 "Apple developers will still have access to System 7.1 through the
  monthly Developer CD series, but they may use it only for testing
  and development purposes."              - AppleDirect, Nov/Dec 92