Re: Checking a method for parameter types via SEL
Re: Checking a method for parameter types via SEL
- Subject: Re: Checking a method for parameter types via SEL
- From: Tommy Nordgren <email@hidden>
- Date: Mon, 31 Jul 2006 21:31:20 +0200
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
------------------------------------------------------
"Home is not where you are born, but where your heart finds peace" -
Tommy Nordgren, "The dying old crone"
email@hidden
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