Re: Porting to 64Bit -descriptionForInstanceMethod:

[David Chisnall]

Wow, this is really old code!

On 18/06/2019 12:59, Andreas Höschler wrote:
> *SRProxy.m:419:29: **warning: **instance method 
> '-descriptionForInstanceMethod:' not found (return type defaults to 
> 'id') [-Wobjc-method-access]*
>           types = [_protocol 
> descriptionForInstanceMethod:aSelector]->types;
> *                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~*
> */usr/include/objc/Protocol.h:45:12: note: *receiver is instance of 
> class declared here
> @interface Protocol : NSObject
> *           ^*
> *SRProxy.m:419:70: **error: **no member named 'types' in 'struct 
> objc_object'*
> *
> *

With the 'Modern' Objective-C ABI (circa 2006) on Apple platforms, the 
only option on 64-bit and the default for a very long time on 32-bit, 
Protocol no longer has any methods exposed on it.  This means:

- descriptionForInstanceMethod: is gone.  Don't use it, use the runtime 
functions instead.  There is no point paying the overhead of an 
Objective-C message send for a function where all of the types are known 
at compile time.

- The compiler assumes that the nonexistent method 
-descriptionForInstanceMethod: returns id, which is a typedef for struct 
objc_object, which has no fields other than isa (probably not even isa, 
because direct access to isa is also deprecated).

David