Re: -isEqual: equals '==' ?

[Richard Frith-Macdonald]

On Sunday, October 19, 2003, at 06:24 AM, Yen-Ju Chen wrote:

> Hi,
>
>  Is -isEqual: the same as '==' ?

No (though it might be implemented that way for a particular class).

>  Since -isEqual: is defined in NSObject and '==' is in compiler,
>  they seem not the same.
>  Then in NSDictionary, which one does it use to get the object by 
> comparing key ?
>  -isEqual: or '==' ?

the -isEqual: method.

>  From Apple's document, overriding -isEqual: requires overriding -hash.
>  Does it apply in GNUstep ?

Maybe ...
the -isEqual: method compares its argument with the receiver ...
and the actual comparison mechanism used depends on the receiving object
of course.  Some classes may implement it to use the fact that if the 
hash of
the receiver and the has of the argument differ, the two cannot be 
equal.
Other classes may not use the -hash method at all.
You should certainly ensure that -isEqual: and -hash are consistent ... 
so if you
override one you may need to override the other.  Two object which are 
equal
should also have the same hash, though two objects with the same hash 
are
not necessarily equal.