Why is it that sending any selector to a Nil object does nothing, but sending an “invalid” selector to any NSObject raises an exception?

Question

Does anyone know why NextStep/Apple decided to take the \"convenient method\" of doing nothing when passing a Nil object a message, but the \"Java method\" of raising an exc

Answer 1

For everyone's amusement, due to the discussion CodaFi and I were having, here's a quickly-hacked-together way to eat normally unresponded-to messages and have them return nil:

@interface EaterOfBadMessages : NSObject 
@end

@implementation EaterOfBadMessages

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector 
{
    NSMethodSignature * sig = [super methodSignatureForSelector:aSelector];
    if( !sig ){
        sig = [NSMethodSignature signatureWithObjCTypes:"@@:"];
    }
    return sig;
}

- (void)forwardInvocation:(NSInvocation *)anInvocation 
{
    id nilPtr = nil;
    [anInvocation setReturnValue:&nilPtr];
}

@end

int main(int argc, const char * argv[])
{

    @autoreleasepool {

        EaterOfBadMessages * e = [[EaterOfBadMessages alloc] init];
        // Of course, pre-ARC you could write [e chewOnThis]
        NSLog(@"-[EaterOfBadMessages chewOnThis]: %@", [e performSelector:@selector(chewOnThis)]);

    }
    return 0;
}

Please don't use this in real life.