Re: Project Center inspiration sshots

[Björn Giesler]

Hi,

Am 03.01.2005 um 13:19 schrieb Markus Hitter:
> Do you have a link where you have this chart from?

I made it myself, based on the contents of the Smalltalk browser that 
Stefan posted. I guess I should have made that clearer in my mail. So 
what is shown is actually a couple of Smalltalk classes and categories, 
although the displayed method is in ObjC. There are a couple of things 
sorely lacking in the diagram (typed return values, typed arguments, 
etc.), which don't exist in Smalltalk. I understand how this would be 
confusing, but I assumed many people to be familiar with Smalltalk and 
to have seen the screenshots from Stefan's mail, and anyway it's only a 
quick mock-up.

The chart shows a UML class diagram with a couple modifications. The 
dashed rounded rects are class categories. (This is not in UML, IIRC.) 
One of them (Kernel) is open, the other ones are closed. So "Date & 
Time" is a class category containing classes for date and time 
handling. The square boxes are classes with class names, attributes and 
methods. Methods are grouped under arbitrary names ("copying", 
"printing"), like the Smalltalk browser does.

> - The arrwos from "Class" and "Metaclass" ... looks like you have 
> something like multiple inheritance in mind. This is discouraged in 
> OpenStep/Cocoa.

It's not even possible in ObjC, and neither in Smalltalk :-) But you 
understand the arrows the wrong way around. In UML, an arrow like that 
points to the superclass, so Class and Metaclass both inherit from 
Behaviour.

> - "Metaclass" = super class? There is no mention about something 
> "meta" in the whole Cocoa documentation (as of Xcode 1.2).

As I said, this document does not show anything Cocoa-related. It's 
just an example about how I personally could envision OO development.

> - All I know about OOP says, an object is an instance of a class. So, 
> objects don't have methods.

But NSObject has methods. "Object" is just the superclass of 
everything, which would be "NSObject" in Smalltalk. Indeed I haven't 
put any class methods in there. Simply forgot them. Put an imaginary 
"-" in front of all the methods in the "copying" group.

Gruß,
Björn
--
Björn Giesler. UI Fascist, Mac Zealot, Gadget Freak.
Mail: bjoern@giesler.de - Web: http://giesler.de
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We must never take these words too seriously. Words are very important, 
but then if we take them too seriously, we destory everything.

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