Question

I’m trying to override a getter in Objective-C. I have two classes, First and Second, like:

First.h:

@interface First : MashapeResponse {
    NSString* message;
}

@property(readwrite, retain) NSString* message;

@end

First.m:

#import "First.h"

@implementation First

@synthesize message;

@end

Second.h:

#import "First.h"

@interface Second : First

-(NSString*) message;

@end

Second.m:

#import "Second.h"

@implementation Second

-(NSString*) message {
    return [NSString stringWithFormat:@"%@%@", @"Message is ", message];
}

@end

I’m trying to execute the following code, but it seems like the overridden method in Second is never executed.

First* first = [[First alloc] init];
[first setMessage:@"hello"];
NSLog(@"%@", [first message]); // "hello" expected

Second* second = (Second*) first;
NSLog(@"%@", [second message]); // "Message is hello" expected, but it's still "hello"

Answer 1

You’re actually casting a First as a Second (which is bad form); but the underlying type is still First, that’s why you see the original message (from First). Alloc a Second, and it should work as expected.