introduction to objective c

[evan]

here are some very simple classes I'm trying to get working just so I can move on from there to more complicated things:

listtest.m

#import <stdio.h>
#import "lst.h"

int main (void) {
Lst *l = [Lst new];
[l x: 10];
printf("%i\n", [l x]);
return 0;
}


lst.h

#import <objc/Object.h>

@interface Lst : Object
{
@private
int x;
}
- (id) x: (int) x_value;
- (int) x;
@end


lst.m

#import "lst.h"

@implementation Lst

- (id) x: (int) x_value {

x = x_value;
return self;
}

- (int) x {
return x;
}

@end


and here's what happens:

Evan-Daviss-iMac:code Evan$ gcc *.m -lobjc
listtest.m: In function ‘main’:
listtest.m:10: warning: ‘Lst’ may not respond to ‘+new’
listtest.m:10: warning: (Messages without a matching method signature
listtest.m:10: warning: will be assumed to return ‘id’ and accept
listtest.m:10: warning: ‘...’ as arguments.)


this code very closely resembles the tutorial I'm following which also does not have an init method, so i'm being led to believe it's not entirely necessary... and even when I try to add one it doesn't work, and gives the same warning with alloc and init that it does with new in this example. ugh, why is this so difficult!!

[Majost]

Wow, what tutorial are you following? It looks like it might be a Linux/GNU tutorial. The base Object class really doesn't do much by default... it doesn't even retain/release.

I would strongly recommend a tutorial that works with Apple's implementation of NSObject, especially if you want to eventually make an OS X or iPhone app. The easy solution is to #import <Cocoa/Cocoa.h> instead of objc/Object.h, and then have your Lst class extend NSObject instead of Object.

And then give up on that tutorial. There are a bunch of great Apple-style Objective-C tutorials around on the web. cocoadevcentral.com and macresearch.org both are good places to start. I'm sure there's more, too.

Edit: Oh, I figured it out. Apple ripped the guts out of the Object implementation in Objective-C 2.0. If gcc is compiling for Objective-C 2, Object will only respond to +class and -isEqual:. I don't know if there's a way to go back to the 1.x implementation.

[Wyatt]

Apple's documentation has a lot of good stuff, too, including some getting started guides for Mac, iPhone and Objective-C. I just started working through an iPhone development class from Stanford on iTunes U, and I'm enjoying that so far.

[evan]

http://en.wikibooks.org/wiki/Objective-C_Programming/syntax

Unfortunately this is for a class so when they run the final assignment submission it will be in Linux so I can't really jump ship and use apple's specialized obj c 2.0 stuff :(

Thanks for the info about the gcc compiler I'll bring that up in class today

[Majost]

Aha! Got it!

You simply need to use the old 4.0 version of gcc.

$ gcc-4.0 *.m -lobjc

[evan]

I love when it's a one line fix :)

why would apple take out all the Object functionality in their update to Obj-c? Seems an odd thing to do

[Majost]

Yeah, I was curious about that, too. I tried searching, but searching on 'Object' sucks. One very nice side-effect of no namespaces: NSObject is a beautiful search term.