Re: Is it possible for a subclass to set the ivar of its base class?

[Manoah F. Adams]

On Sep 24, 2016, at 08:11:00, Patrick J. Collins wrote:

I am trying to change the behavior of a library by subclassing one  
of the
files, but am finding this is not working because I can't access  
(change) one

of the internal instance variables.

To illustrate my problem:

 Rofl *rofl = [[Rofl alloc] init];
 [rofl otherSetWut:123];
 [rofl speak];

 

   @implementation Lol {
   int _wut;
   }

   -(void)setWut:(int)wut {
   _wut = wut;
   // side effects I do not want.
   }

   -(void)speak {
   NSLog(@"so wut up? %i", _wut);
   }

   @end

 

   @implementation Rofl {
   int _wut;
   }

   -(void)otherSetWut:(int)wut {
   _wut = wut;
   }

   @end

 


When I run this, I get 0 instead of 123.  Is there a way I can get  
access to the _wut ivar in the base class so that I will

How can I make it so that I will get the desired 123 output?

Thanks!

Patrick J. Collins
http://collinatorstudios.com





For one thing, I would avoid knowingly shadowing an iVar, as I don't  
see a benefit, and indeed, as I see it, it is preventing you from  
reaching the one the superclass is using.
More importantly, if the superclass is indeed providing unwanted side- 
effects, then there is likely a design issue with that class -- in so  
far as the setter is doing too much.

They should be using a separate method for actual operations.

Further, bypassing the setter, when the rest of the superclass uses it  
(which is likely, though not necessarily true) will cause the super- 
class's code to behave improperly,
so before using the runtime to directly modify it, check the bass  
class code to make sure it is not internally using the setter.






Manoah F. Adams
mhfad...@federaladamsfamily.com
federaladamsfamily.com/manoah

This message is signed with a certificate and-or PGP key.
Disregard any unverified messages from this address.
Email Certificates for personal use can be obtained from Comodo at
 

For PGP/GPG key usage and tools, see 
===






smime.p7s
Description: S/MIME cryptographic signature
 ___
Do not post admin requests to the list. They will be ignored.
Objc-language mailing list  (Objc-language@lists.apple.com)
Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/objc-language/archive%40mail-archive.com

This email sent to arch...@mail-archive.com

Re: Is it possible for a subclass to set the ivar of its base class?

[Quincey Morris]

On Sep 24, 2016, at 12:15 , Patrick J. Collins  
wrote:
> 
> There's no way to do this without duplicating tons of their code?

You can’t add a method (setOtherWut) to the base class in the subproject? That 
would be easier than mucking with the run-time. ___
Do not post admin requests to the list. They will be ignored.
Objc-language mailing list  (Objc-language@lists.apple.com)
Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/objc-language/archive%40mail-archive.com

This email sent to arch...@mail-archive.com

Re: Is it possible for a subclass to set the ivar of its base class?

[Quincey Morris]

On Sep 24, 2016, at 08:11 , Patrick J. Collins  
wrote:
> 
>@implementation Lol {
>int _wut;
>}
> 
>-(void)setWut:(int)wut {
>_wut = wut;
>// side effects I do not want.
>}

How do you know this *is* the implementation in the base class? How do you know 
there *is* a private variable called “_wut”, or its type, or what value it 
actually contains, or if there are any other variables that must be set 
consistently whenever the value of the “wut” property changes?

I don’t see how you can safely make your change without seeing the source code 
of the base class, and it you have access to the source code you’d be better 
off making a custom library.

 ___
Do not post admin requests to the list. They will be ignored.
Objc-language mailing list  (Objc-language@lists.apple.com)
Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/objc-language/archive%40mail-archive.com

This email sent to arch...@mail-archive.com