/** * hello_world.m * $gcc -framework Foundation hello_world.m -o hello_world */#import <Foundation/NSObject.h>#import <Foundation/NSString.h> @interface HelloWorld : NSObject{ NSString* message;}- (NSString *) message;- (void) say:(NSString *)msg;@end @implementation HelloWorld- (NSString *) message { return message;}- (void) say:(NSString *)msg { NSLog(@"%@", msg);}@end int main(){ HelloWorld