The Tech Help You Need

[Jay Sachs <jay@xxxxxxxxx>]

On Dec 28, 2006, at 12:06 PM, Burak Emir wrote:
> On 12/28/06, Jay Sachs <jay@xxxxxxxxx> wrote:
> On Dec 28, 2006, at 10:49 AM, Burak Emir wrote:
>
> > do you think it would make sense to define Some.equals method such
> > that Some(x) == x?
>
> But then wouldn't Some(None) == None ?
>
> Good point. One could make a special case for None.
>
> Options of options are quite rare, and a big obstacle to  
> optimization of option types, but since we have them, it would  
> surely be very confusing to have Some(None) == None. Also Some(Some 
> (x)) should not be == Some(x). So here's what is meant.
>
> case class Some[a](x:a) extends Option[a]{
>   def equals(y:Any) = y match {
>      case None => false
>      case Some(z) => x == z
>      case z => x == z
>   }
> }
>
> It's just a proposal, if nobody ever wished for this thing, it's  
> probably not worth including.

I think it's difficult if not impossible to get the semantics right.  
You've eliminated Some(Some(x)) == Some(x), but what if the nested  
"Some" is inside a list:

  Some( List(Some(3)) : List[Any] ) == List(3) : List[Any] )

Per your definition above, this evaluates to

  List(Some(3)) == List(3)

which recursively will invoke Some.== and return true.