Re: Guidance for Cocoa's steep learning curve

FROM : Jens Alfke
DATE : Thu May 15 16:59:48 2008

On 14 May '08, at 10:16 PM, David Wilson wrote:

> 3) Instance methods (with the -) are virtual functions. Class 
> methods (with the +) are static functions.


Class methods aren't exactly like static functions, because they're 
still dynamically dispatched and can be overridden by subclasses.

A closer analogy is to think of there being a singleton "class object" 
for every class (which is what -class returns), and the class methods 
are instance methods of those class objects. The class objects have an 
inheritance hierarchy that parallels the class hierarchy, so if B is a 
subclass of A, B's class object will be a subclas of A's class object.

(For more detail, look up "metaclass"; I'm sure there's an abstruse 
Wikipedia article about it. The concept goes back to Smalltalk-80, on 
which Objective-C's runtime model and syntax were based.)

—Jens

PS: In regards to the thread subject, I didn't find Cocoa to have a 
steep learning curve. I took a training class and was amazed at how 
easy it was to learn, and to build sophisticated apps with, compared 
to every other GUI API or framework I'd used.