Re: isEqual: and hash in NSDate

[Richard Frith-Macdonald]

On 2005-07-22 15:57:03 +0100 Adrian Robert <address@hidden> wrote:


> This really seems like a hack (not that it's any worse than the current 
> state 
> :).  Couldn't the implementations of -hash and -isEqual be aligned without 
> this loss of information?  E.g. something like [warning, sloppy 
> first-attempt 
> code here]:
>
> -isEqual:other
>   return abs(selfVal - other->selfVal) < epsilon;
>
> -hash
>   return selfVal / epsilon;
> (or maybe (selfVal + epsilon/2.0) / epsilon)

No ... each NSDate has to have its own independent hash ... but (following 
the OpenStep spec) dates are equal if they are within a second of each 
other.

That means that with dates d1, d2, d3 which have offsets from the reference 
date of 0.0, 0.7 and 1.4 seconds,
d1 is eqal to d2 and d2 is equal to d3 but d1 is not equal to d3 ... a 
rather counterintuitive behavior!

So ... as long as we stick to the OpenStep spec, we can't use dates as 
dictionary keys.

I think we should move with MacOS-X here rather than sticking to OpenStep.