Re: Stupid Cocoa question. How can you tell if the object you are looking at is a property or an ivar?
Re: Stupid Cocoa question. How can you tell if the object you are looking at is a property or an ivar?
- Subject: Re: Stupid Cocoa question. How can you tell if the object you are looking at is a property or an ivar?
- From: Graham Cox <email@hidden>
- Date: Thu, 21 May 2015 09:53:28 +1000
> On 21 May 2015, at 6:50 am, Michael David Crawford <email@hidden> wrote:
>
> In my own code I started with nothing but ivars, but changed some of
> them to properties while neglecting to remove the original ivar. This
> leaves me somewhat in the same situation as you.
Nothing wrong with that, AS LONG as you remember to add the @synthesize foo = myOriginalIvar in your implementation. Problem is, it’s not a compile-time error if you forget. It might not even be a runtime error, but it’s very likely a bug anyway, because when you think you’re manipulating < myOriginalIvar >, in fact it’s manipulating a hidden _foo ivar. At its most benign, this is just a minor waste of space for the < myOriginalIvar > storage, but if code (and legacy code is quite likely to do this) is sometimes accessing the ivar directly, and sometimes through the property, you have a very, very definite and insidious bug.
Frankly, (and I have said this before more than once) the design of autosynthesizing properties, added as it was later to properties themselves, is a nasty way to shoot yourself in the foot and not even realise it. Caught me out numerous times.
You can enable the warning CLANG_WARN_OBJC_MISSING_PROPERTY_SYNTHESIS (“Implicit Synthesized Properties” in build settings) to at least be told when you pulled the trigger.
—Graham
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