Provide before/after aspects on Cocoa objects (for http://stackoverflow.com/questions/9267727/)

main.m

#import <Foundation/Foundation.h>

@interface AspectProxy : NSProxy {
    id target_;
}

- (id)initWithTarget:(id)target;

@end

@implementation AspectProxy

- (id)initWithTarget:(id)target {
    target_ = [target retain];
    return self;
}

- (void)dealloc {
    [target_ release];
    [super dealloc];
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel {
    return [target_ methodSignatureForSelector:sel];
}

- (void)forwardInvocation:(NSInvocation *)inv {
    SEL sel = [inv selector];
    NSLog(@"forwardInvocation for: %@", NSStringFromSelector([inv selector]));
    if (sel == @selector(aspectBefore:) || sel == @selector(aspectAfter:)) {
        return;
    }
    if ([target_ respondsToSelector:@selector(aspectBefore:)]) {
        [target_ performSelector:@selector(aspectBefore:) withObject:inv];
    }
    [inv invokeWithTarget:target_];
    if ([target_ respondsToSelector:@selector(aspectAfter:)]) {
        [target_ performSelector:@selector(aspectAfter:) withObject:inv];
    }
}

@end

@interface Test : NSObject

@property (nonatomic, copy) NSString *text;

- (void)someFunction;

@end

@implementation Test

@synthesize text;

- (id)init {
    if (self = [super init]) {
        return [[AspectProxy alloc] initWithTarget:[self autorelease]];
    }
    return self;
}

- (void)dealloc {
    self.text = nil;
    [super dealloc];
}

- (void)aspectBefore:(NSInvocation *)inv {
    NSLog(@"before %@", NSStringFromSelector([inv selector]));
}

- (void)aspectAfter:(NSInvocation *)inv {
    NSLog(@"after %@", NSStringFromSelector([inv selector]));
}

- (void)someFunction {
    NSLog(@"some function called");
}

@end


int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
    
    Test *x = [[[Test alloc] init] autorelease];
    [x someFunction];
    x.text = @"test";
    NSLog(@"x.text='%@'", x.text);
    
    [pool drain];
    return 0;
}