Re: Re: Finding out if an NSArray's contents are all equal

FROM : Michael Ash
DATE : Sun Jul 23 05:07:08 2006

On 7/22/06, patrick machielse <<email_removed>> wrote:
> Op 23-jul-2006, om 00:53 heeft Andre het volgende geschreven:
>
> >  patrick machielse wrote:
> >
> >> @implementation NSArray (IdenticalObjects)
> >> - (BOOL)allObjectsIdentical
> >> {
> >>    return [[NSSet setWithArray:self] count] == 2;
> >> }
> >> @end
>
> This should of course have read:
>
> >>    return [[NSSet setWithArray:self] count] == 1;  // _ONE_!
>
> A better/nicer/more general idea would be to use:
>
> - (unsigned)numberOfDistinctObjects
> {
>      return [[NSSet setWithArray:self] count];
> }


I feel compelled to point out that this will not work for all arrays.
In particular, any arrays which contain objects whose -hash method is
incorrectly implemented will potentially return incorrect (inflated)
counts for the sets. This could happen if, for example, you have a
custom class that overrides -isEqual: but doesn't override -hash to
return a hash based on the equality criteria.

I would consider this a bug in the custom class, though. If you
override -isEqual: then you should always override -hash to match,
exactly because of this sort of problem.

Mike