How to allocate a new object without Foundation?

Question

I want to construct a simple Objective C program without Foundation. I tried:

#include <stdio.h>

@interface Foo{
    char * bar;
}
-(void)hello;
@end

@implementation Foo
-(void)hello {
    printf("Hello world!");
}
@end

int main(){
    Foo * foo = [Foo alloc];
    return 0;
}

Then it tells me Foo may not respond to +alloc and autorelease called without pool...

How can I initialize an object without using alloc from Foundation?

Answer 1

It's very simple to create a new object without using alloc from Foundation. The Objective-C runtime library itself provides functions that allow one to allocate objects from classes and deallocate them later, so that you need no extra library to create and destruct objects.

The function id class_createInstance(Class cls, size_t extraBytes) receives a class object, from which to allocate a new object, and an integer, which is almost always zero, and returns a new instance of cls.

Similarly, the function id object_dispose(id obj) takes an Objective-C object, calls the C++ destructor of every C++ object instance variable, removes existing associated references and frees it.

class_createInstance and object_dispose are both declared in /usr/include/objc/runtime.h.

So, you can implement your own +alloc and -dealloc methods. Your program would look like this:

#include <stdio.h>
#include <objc/runtime.h>

@interface Foo{
    char * bar;
}
+(id)alloc;
-(void)hello;
@end

@implementation Foo
+(id)alloc {
    // Returns a new 'Foo' object. In this case, 'self' is a 'Foo' class object,
    // whose type is 'Class', as required by `class_createInstance`.
    return class_createInstance(self, 0);
}
-(void)dealloc {
    object_dispose(self);
}
-(void)hello {
    printf("Hello world!");
}
@end

int main(){
    Foo *foo = [Foo alloc];
    [foo hello];
    [foo dealloc];

    return 0;
}

Compile it as you normally do:

gcc Foo.m -o Foo -lobjc

That's all!

Answer 2

You can write Objective C without Foundation, but of course you may end up re-inventing the wheel to some degree.

As millimoose suggests, you could use the GNUStep Objective C runtime.

For more info, see:

• http://jongampark.wordpress.com/2008/05/02/objective-c-without-cocoa/
• How do you create a simple Objective-C command line project in Xcode
• https://softwareengineering.stackexchange.com/questions/101832/why-is-objective-c-not-widely-used-beyond-cocoa-environments
• How does one use Obj-C 2.0 with GNUstep?