Re: Objective-C and it's future

FROM : Rob Ross
DATE : Sat Jul 08 03:15:57 2006

>
> NSString *str = [[NSData alloc] init];
>
> because both `NSData' and `NSString' have `init' methods, and 
> `init' methods return an object of type `id', which is NOT 
> statically typed.
>


This looks like the kind of bug that would be easy to make, 
especially with class names that are very similar. I guess you won't 
find out until you send the object a message at runtime that it can't 
process; then you'd have to hunt back through the stack trace to see 
how you declared the object. I suppose in practice, it wouldn't be 
that hard to debug this kind of error.


> For more egregious violations, like for example ...
>
> Cat *cat = [[Cat alloc] init];
> [cat bark];
>
> ... the compiler will throw up a warning and tell you that `cat' 
> may not respond to the selector `bark'.
>


Well I'm glad at least it does that!


>
>

>> So my understanding is you can have the best of both worlds. Or 
>> have I misunderstood something?
>>

>
> Not quite. Objective-C is pretty well entrenched in the runtime.
>
> You have to remember that you're NOT actually "calling a method" 
> when working with Objective-C objects. You are sending them 
> messages. Think about it this way. If language objects are people, 
> then C++ objects are basically puppets. You don't tell them to do 
> something; you just pull the string, and they do it. Objective-C 
> objects are more independent. You TELL them that you'd like 
> something done, and they'll do it if they can.
> --
>


That's interesting, because I remember a point long ago when I was 
first learning OO programming (in C++), that I understood the concept 
of "message passing", but that C++ didn't really implement that (nor 
does Java): you're invoking a method, not passing a message. I was 
always puzzled by the definition because the languages I used didn't 
really seem to behave as described. It's nice to finally meet a 
language that does what I intuitively understood "message passing" to 
be.

Rob