Re: error: synthesized properties 'foo' and 'bar' both claim ivar 'myIvar'
Re: error: synthesized properties 'foo' and 'bar' both claim ivar 'myIvar'
- Subject: Re: error: synthesized properties 'foo' and 'bar' both claim ivar 'myIvar'
- From: Quincey Morris <email@hidden>
- Date: Thu, 18 Nov 2010 02:28:39 -0800
On Nov 18, 2010, at 00:43, Andreas Grosam wrote:
> Found this bug report related to this issue and the following explanation:
> <http://www.mail-archive.com/email@hidden/msg03631.html>:
>
>> --- Comment #1 from Fariborz Jahanian <email@hidden> 2009-06-22 21:34:42 ---
>> This is part of the language spec. and cannot be changed. Two properties cannot use the same 'ivar'
>> for their setter/getter synthesis. This is deemed necessary because it will be extremely error prone to
>> allow the ivar changed via unrelated property operations.
>
>
> Error prone for whom? The compiler writer or the programmer?
>
> IMHO, if this is error prone for the programmer, the rationale doesn't seem to be reasonable enough to me, especially when the properties are readonly.
Really, there's no such thing as a readonly property, only a property that may or may not have a setter as well as a getter, and the compiler cannot determine absolutely whether or not there is a setter. (That's a consequence of the equivalence of @property-related and old-style property definition syntax, at least.) If setters are present at runtime, @synthesized ivar-sharing would certainly break KVO, and possibly would break @synthesized property atomicity.
If ivar sharing is not allowed for @synthesize, the penalty to the programmer is having to write one set of accessors manually -- a trivial task. If ivar sharing were allowed, the penalty would be to open up the code to a number of KVO notification and multi-threading issues, especially when more code was added later -- a distinctly non-trivial burden.
Are you sure the rationale is so insufficient?
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