Re: Subclass
Re: Subclass
- Subject: Re: Subclass
- From: Marco Scheurer <email@hidden>
- Date: Sat, 14 Jun 2003 16:40:12 +0200
On Saturday, June 14, 2003, at 10:22 AM, Sailor Quasar wrote:
On Friday, June 13, 2003, at 11:14 PM, Marco Scheurer wrote:
Is there another way to do this in Obj-C.
At runtime. You can implement these methods to send a
doesNotRecognizeSelector: message. Or, there used to be a
subclassResponsibility: method in NSObject, but it's not there
anymore. You could create one that raises a meaningful exception and
use it.
With all due respect to the Obj-C veterans on these lists, and
aplogies for cross-posting to cocoa-dev, the functionality requested
by the original poster of this thread is one of several minor OO bits
that C++ has but Obj-C does not that I feel would be better off there:
1. As noted, enforcement of pure virtual base classes.
The enforcement looks like on paper, but is useless in practice, as
this is never a cause of problems. And as described above, it *can* be
enforced: at runtime instead of compile time, just like for dynamic
typing. This is Objective C.
2. The ability to declare methods protected or private I'm aware it's
quite possible to declare private methods as a category within the
class' source file so that the selectors are not published to client
code. For private methods this is fine since it prevents unwanted code
from easily using them, but for protected methods it's a nusiance at
best and not doable at worst.
I don't miss them since I think that private and protected are an
hindrance to flexibility and reuse. To decide that a piece of code will
never need to be used differently than what I know now is presumptuous.
Java's final falls in the same category.
3. The ability to declare static instance vars (instance vars that are
part of the class object rather than of any instance of that class).
If I've missed this functionality somewhere, please tell me where it
is. I generally use globals to emulate it, which I personally feel is
bad style.
What's missing is real class variables (static vars are available as in
plain C and often used as a workaround for class variables).
Marco Scheurer
Sen:te, Lausanne, Switzerland
http://www.sente.ch
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