interposing on objc sample

main.m

// (C)2011 to3oo mi2ukam1 tmiz.net
//
// interposing on objc sample
// $ g++ main.m -framework cocoa
// $ ./a.out 
// 2011-12-20 12:12:37.159 a.out[533:903] hello
// 2011-12-20 12:12:37.164 a.out[533:903] world

#include <cocoa/cocoa.h>
#include <objc/objc-class.h>

// --- example instead of existing class

@interface AObject : NSObject {
    
};

-(void)sayHello;

@end

@implementation AObject

-(void)sayHello
{
    NSLog(@"hello");
}
@end

// 

@implementation AObject(DYNA)

-(void)sayHello_new
{
    [self sayHello_new];
    NSLog(@"world");
}

@end

void interpose()
{
    Class aobj_class = objc_getClass("AObject");
    Method a = class_getInstanceMethod(aobj_class,
				       @selector(sayHello));
    Method b = class_getInstanceMethod(aobj_class,
				       @selector(sayHello_new));
    method_exchangeImplementations(a, b);
}

int main() {
    interpose();
    id aobj = [[AObject alloc] init];
    [aobj sayHello];
    [aobj release];
    return 0;
}