Comments on: An introduction to Cocoa and Cocoa Touch http://boredzo.org/blog/archives/2010-02-03/cocoa-and-cocoa-touch-intro The personal weblog of Peter Hosey. Wed, 09 May 2012 18:26:35 +0000 hourly 1 http://wordpress.org/?v=3.1 By: Peter Hosey http://boredzo.org/blog/archives/2010-02-03/cocoa-and-cocoa-touch-intro/comment-page-1#comment-301502 Peter Hosey Wed, 03 Feb 2010 20:54:22 +0000 http://boredzo.org/blog/?p=1241#comment-301502 <blockquote>* "Ownership" has a specific meaning here that is not quite like the non-programming meaning of the word. An object can have multiple owners, …</blockquote> That's true in real life as well. Things, both physical and imaginary, can be co-owned by multiple owners. (IANAL.) <blockquote>… and be owned multiple times by the same owner.</blockquote> True, but unusual. Even so, important to conceptual understanding. I'll think about how to include this. <blockquote>* You should be aware of the possibility of retain cycles.</blockquote> Good suggestion. <blockquote>Contrary to common misconception, methods do not have "named" parameters. If they did you would not be able to have a method called performSelector:withObject:withObject:. Which parameter would be the one named "withObject"?</blockquote> Both of them. I get what you're saying, though: <code>performSelector:withObject:withObject:</code> is the complete name (selector) of the method, not simply the name followed by two arguments. This is worth including. <blockquote>It's perfectly okay to send messages to nil, and to simplify code accordingly. This is something that people new to Objective-C seem to have trouble getting their heads around.</blockquote> Also, a variable will not magically become <code>nil</code> if the object whose pointer is in it dies. As such, you can't test the variable whether the variable contains <code>nil</code> to test whether the object is still alive. (This is most likely from people conflating the variable with the object.) Good suggestions all. Thank you.

* “Ownership” has a specific meaning here that is not quite like the non-programming meaning of the word. An object can have multiple owners, …

That’s true in real life as well. Things, both physical and imaginary, can be co-owned by multiple owners.

(IANAL.)

… and be owned multiple times by the same owner.

True, but unusual. Even so, important to conceptual understanding. I’ll think about how to include this.

* You should be aware of the possibility of retain cycles.

Good suggestion.

Contrary to common misconception, methods do not have “named” parameters. If they did you would not be able to have a method called performSelector:withObject:withObject:. Which parameter would be the one named “withObject”?

Both of them.

I get what you’re saying, though: performSelector:withObject:withObject: is the complete name (selector) of the method, not simply the name followed by two arguments. This is worth including.

It’s perfectly okay to send messages to nil, and to simplify code accordingly. This is something that people new to Objective-C seem to have trouble getting their heads around.

Also, a variable will not magically become nil if the object whose pointer is in it dies. As such, you can’t test the variable whether the variable contains nil to test whether the object is still alive. (This is most likely from people conflating the variable with the object.)

Good suggestions all. Thank you.

]]> By: Andy Lee http://boredzo.org/blog/archives/2010-02-03/cocoa-and-cocoa-touch-intro/comment-page-1#comment-301495 Andy Lee Wed, 03 Feb 2010 20:28:58 +0000 http://boredzo.org/blog/?p=1241#comment-301495 Great collection of bullet points that every Cocoa developer should internalize. A handful of others come to mind (of course it's up to you where to draw the line -- otherwise the list would never end). Regarding memory management: * "Ownership" has a specific meaning here that is not quite like the non-programming meaning of the word. An object can have multiple owners, and be owned multiple times by the same owner. * You should be aware of the possibility of retain cycles. Regarding Objective-C (though it seems you're addressing framework issues more than language issues): * Contrary to common misconception, methods do not have "named" parameters. If they did you would not be able to have a method called performSelector:withObject:withObject:. Which parameter would be the one named "withObject"? * It's perfectly okay to send messages to nil, and to simplify code accordingly. This is something that people new to Objective-C seem to have trouble getting their heads around. Great collection of bullet points that every Cocoa developer should internalize. A handful of others come to mind (of course it’s up to you where to draw the line — otherwise the list would never end).

Regarding memory management:

* “Ownership” has a specific meaning here that is not quite like the non-programming meaning of the word. An object can have multiple owners, and be owned multiple times by the same owner.

* You should be aware of the possibility of retain cycles.

Regarding Objective-C (though it seems you’re addressing framework issues more than language issues):

* Contrary to common misconception, methods do not have “named” parameters. If they did you would not be able to have a method called performSelector:withObject:withObject:. Which parameter would be the one named “withObject”?

* It’s perfectly okay to send messages to nil, and to simplify code accordingly. This is something that people new to Objective-C seem to have trouble getting their heads around.

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