Re: isEqual: and hash in NSDate

[Richard Frith-Macdonald]

On 2005-07-22 18:03:38 +0100 Markus Hitter <address@hidden> wrote:

> Regarding to this, in my little recherche yesterday, I couldn't find  any 
> difference between -isEqual:, -isEqualTo: and -isEqualToDate:.  The last 
> type 
> is supported by some common other classes as well, e.g.  -isEqualToString:, 
> -isEqualToNumber:, ...
>
> My impression was, -isEqual: is meant for coarse comparisons or hash 
> comparisons. But that's an impression only.

I don't know of any -isEqualTo: method.  AFAIK there is only -isEqual: or 
the variants with the class in the name (-isEqualToString:, 
-isEqualToNumber: etc)

> Since it's interesting for coding in GNUstep/Cocoa as well: Does  anybody 
> know what's the difference between the members of these  trios? Why does 
> -isEqualTo: exist at all

I don't believe it does.  At least, not in GNUstep.

> and why doesn't NSDate  simply override -isEqual: 
> instead of introducing -isEqualToDate:?

It does override -isEqual:

My understanding is that the variants with the class name in them are 
intended as optimisations ... where the method may assume that what it gets 
as an argument is a member of the correct class, thus avoiding to need to 
check what class the argument belongs to.

Thus, for NSDate, -isEqual: might be implemented as -

- (BOOL) isEqual: (id)anObject
{
  if ([anObject isKindOfClass: [NSDate class]])
    {
      return [self isEqualToDate: (NSDate*)anObject];
    }
  return NO;
}

> Is it just an historical artefact? Should I file a bug report at  Apple to 
> get rid of at least -isEqualTo:?

Maybe ... I don't know about it.