Re: Another Gnarly Objective-C Question!
Re: Another Gnarly Objective-C Question!
- Subject: Re: Another Gnarly Objective-C Question!
- From: John McCall <email@hidden>
- Date: Wed, 13 Mar 2013 10:13:20 -0700
On Mar 13, 2013, at 2:13 AM, Jean-Daniel Dupas <email@hidden> wrote:
> Le 13 mars 2013 à 01:55, Wim Lewis <email@hidden> a écrit :
>> On 12 Mar 2013, at 2:08 AM, Graham Cox wrote:
>>> in a + method, [self class] === self. Once you've got that, you've got it.
>>>
>>>
>>>
>>> You're overthinking this.
>>>
>>> A class method is just an instance method of the class object. No magic at all. So all this confusion you've caused yourself about [super class] and so on is wholly unnecessary to correctly use class methods.
>>
>> To be very slightly pedantic, the only magic here is 'super' --- sending a message to super (which you can only do from a method implementation) is special syntax that searches for the method starting with the implementation's class's superclass, rather than at the receiver's actual class. Everything else is non-magic. (In general, that's been one of the strengths of ObjC: very little magic.)
>>
>
> To be ever more pedantic, there is other magic involved when sending a message to a class.
> If there is no class method that matches the selector, the runtime will then search for instance methods of the root class.
Note that this isn't "magic" really; it's a quirk of the type system (both formal and dynamic). The root metaclass is a subclass of the root class.
This can be problematic if you really want your root class to have a layout that's bigger than just an isa field, because the ABI and runtime just hardcode the layout of classes and there is no room for extra fields there — thus you need to be sure that anything using your extra fields is never invoked on a class object.
John.
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