Can I do a fast enumeration directly via a property?

Question

if I have a property

@property (nonatomic, retain) NSArray* myArray;

Can I do ? And if yes why does this work ?

for (id object in self.myArray)
    ;

Or do I need to do ?

NSArray* r = self.myArray;
for (id object in r)
    ;

Did you try it? You could've found the answer in about 20 seconds. — Dave DeLong, Feb 10 '11 at 15:05
Actually I'm more in interested in why it works. Is it a compiler optimization ? How can the loop now that the self.myArray is always the same ? — CodeFlakes, Feb 10 '11 at 15:19

Cthutu · Accepted Answer · 2011-02-10T16:16:54.953

2

It works because self.myArray is syntactical sugar for [self myArray], which is generated by the @synthesize keyword. So really you're doing:

for (id object in [self myArray])

And the return value of [self myArray] implements the fast enumeration protocol so the for..in syntax can work on it.

Does that make things clearer?

edited Feb 10 '11 at 16:16

answered Feb 10 '11 at 15:49

Cthutu

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I would also add that a standard read/writeable property has two functions generated by the @synthesize: myArray and setMyArray. Also this information can be found at http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/Articles/ocProperties.html – Cthutu Feb 11 '11 at 20:16

score 1 · Answer 2 · answered Feb 10 '11 at 15:48

Yes you can use fast enumeration like that. To answer the question from your comments, I believe that the fast enumeration protocol will throw an exception if you modify your array property during enumeration.

http://www.mikeash.com/pyblog/friday-qa-2010-04-16-implementing-fast-enumeration.html

score 0 · Answer 3 · answered Feb 10 '11 at 14:52

0

You can definitely go for for(id object in self.array)

answered Feb 10 '11 at 14:52

iHS

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Can I do a fast enumeration directly via a property?

3 Answers3