Re: Checking a method for parameter types via SEL

FROM : Tommy Nordgren
DATE : Mon Jul 31 21:31:20 2006

Jul 31, 2006 kl. 8:49 PM skrev Bill Bumgarner:

>
> On Jul 31, 2006, at 11:23 AM, Tommy Nordgren wrote:
>

>> Can someone who have been using cocoa long please tell me how to 
>> do this?
>> The signature should be like this:
>> -(BOOL) aMethod: (id) owner;

>
> What, exactly, are you trying to do?
>

   This, to be extended with further methods:
@implementation NSCoder (ConditionalCoding)

-(void) encodeObject:(id) obj onCondition:(SEL) cond withOwner: (id) 
owner
{
   BOOL strongCode = NO;
   NSMethodSignature * sign = [obj methodSignatureForSelector:cond];
   if (sign == nil) {
       strongCode = YES;
   } else {
       if ([sign numberOfArguments] == 3 &&
           strcmp([sign getArgumentTypeAtIndex:2],@encode(id)) == 0 &&
           strcmp([sign methodReturnType] , @encode(BOOL)) == 0) {
           int i = (int)  objc_msgSend(obj,cond,owner);
           strongCode = i ? YES: NO;
       }
   }
   if ( strongCode) {
       [self encodeObject: obj];
   } else {
       [self encodeConditionalObject:obj];
   }
}
@end
I welcome any comment on the code
> The Obj-C runtime supports introspection and you can grab the 
> method signature and then rip it apart to deduce parameter and 
> return types.  To a degree;  you lose with complex C types and 
> certain other parameter types.
>
> I would suggest poking through the source code for one of the 
> various Obj-C bridges to see the full details;  PyObjC, F-Script 
> (Smalltalk-esque), RubyCocoa, and CamelBones (Perl-ObjC) all 
> introspect to do cross language method dispatches.
>
> b.bum
>


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"Home is not where you are born, but where your heart finds peace" -
Tommy Nordgren, "The dying old crone"
tommy.<email_removed>