Question

Please have a look at this code:

Card  *first = [[Card alloc] initWithFace:@"Ace" andSuit:@"Hearts"];
Card *second = [[Card alloc] initWithFace:@"Ace" andSuit:@"Hearts"];

if ([first isEqual:second])
    NSLog(@"Equal");
else
    NSLog(@"Not equal"); //WHY???

NSLog tells me these two objects are not equal. But why? And what should I do to make them equal?

Answer 1

You have to implement your own isEqual: method within the Card class.

This would compare the face and suit of the passed in card object to self, and return an appropriate BOOL value. See here for more details on the base (NSObject) implementation and how you should amend it.

An untested, typed-in-the-browser implementation would be something like:

-(BOOL)isEqual:(id)compareObject
{
    if (self == compareObject)
        return YES;

    if (![compareObject isKindOfClass:[self class])
        return NO;

    Card *compareCard = (Card*)compareObject;
    if ([compareCard.face isEqualToString:self.face] && [compareCard.suit isEqualToString:self.suit])
        return YES;
    else
        return NO;
}

You must also implement hash such that two equal objects return the same hash value.