‘NSAutoreleasePool’ may not respond to ‘-drain’ on Ubuntu

Question

I'm trying to compile the following Objective-C program on Ubuntu Hardy, but for some reasons, I'm getting warnings.

#import <Foundation/Foundation.h>
int main (int argc, char *argv[])
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSLog (@"Hello");
    [pool drain];
    return 0;
}

Output of the compiler:

$ gcc `gnustep-config --objc-flags` -lgnustep-base objc.m
This is gnustep-make 2.0.2. Type 'make print-gnustep-make-help' for help.
Making all for tool LogTest...
 Compiling file objc.m ...
objc.m: In function ‘main’:
objc.m:6: warning: ‘NSAutoreleasePool’ may not respond to ‘-drain’
objc.m:6: warning: (Messages without a matching method signature
objc.m:6: warning: will be assumed to return ‘id’ and accept
objc.m:6: warning: ‘...’ as arguments.)
 Linking tool LogTest ...

Here's the result of the execution:

$ ./a.out
2009-06-28 21:38:00.063 a.out[13341] Hello
Aborted

I've done:

apt-get install build-essential gnustep gobjc gnustep-make libgnustep-base-dev

How do I fix this problem?

Answer 1

Sounds like the class library is out of date in GNUStep, at least in the version you're using -- [NSAutoreleasePool drain] was added in OS X 10.4 IIRC. I don't know anything about GNUStep though, so I don't know if newer libraries are available.

You can work around the problem by replacing 'drain' with 'release'. They do basically the same thing; the 'drain' method was added for use in a garbage-collected app, because 'release' becomes a no-op in that environment.

Answer 2

In my app main loop using GNUStep:

int main(int argc, const char *argv[])
{
    NSAutoreleasePool *pool;
    AppController *delegate;

    pool = [[NSAutoreleasePool alloc] init];
    // ...
    [pool release];
    return NSApplicationMain (argc, argv);
}

Answer 3

First, the simple answer: use -release instead. I believe -drain was added in 10.4 as an alias for -release, and in 10.5 it gained GC-specific behavior of its own. This allows code to use it in 10.5 and still work under 10.4. GNUstep probably doesn't yet have the new functionality.

---

Obviously you're trying out some boilerplate Objective-C code on Ubuntu, but it causes me to wonder what you're hoping to accomplish in the long term. Don't let me deter you if it's just out of curiosity or for the challenge of it. However, if you're planning to use GNUstep to develop Objective-C for serious programming, I would advise against it, for several reasons.

1. Objective-C is an interesting programming language with a number of powerful features, but not significantly more so (by itself) than other object-oriented languages. Objective-C really becomes compelling when you pair it with the cool features in Cocoa and other related frameworks. Apple (primarily) drives those frameworks, and only for Mac/iPhone.
2. Apple generally has the best tools and user experience for Objective-C development. They're also investing heavily in development of LLVM and Clang as a replacement for gcc. This will (an already does) make possible some very cool things that gcc wasn't designed for.
3. GNUstep is an admirable project, but since it depends on volunteers and reverse-engineering new features added by Apple, it always lags behind the state-of-the-art. The new shiny Objective-C features will always start with Apple and (usually) eventually trickle down.
4. Building cross-platform apps could be done in Objective-C, but other languages are much better suited for the task. (I'm not so much of a fanboy as to suggest that Objective-C is the best solution for every problem. Use the best tool you have at hand.)

I'm not saying using languages on something other than their "native platform" is bad. I'm just suggesting that if that's what you're going to do, you should be aware of the potential problems and be sure you're convinced that the pros outweigh the cons.