gistfile1.m

#import <objc/runtime.h>

@interface Foo : NSObject
int ivar;
- (void)doThings;
@end

@implementation Foo
- (id)initWithThings:(int)thing;
{
    if ((self = [super init]))
    {
        ivar = thing;
    }
    return self;
}

- (void)doThings;
{
    NSLog(@"Things %d!", ivar);
}
@end


int main()
{
    Class fooClass = objc_getClass("Foo");
    Foo *foo = class_createInstance(fooClass, 0);
    IMP init = class_getMethodImplementation(fooClass, @selector(initWithThings:));
    init(foo, @selector(init), 1000);
    IMP doStuff = class_getMethodImplementation(fooClass, @selector(doThings));
    doStuff(foo, @selector(doThings));
}