From: Dan Doel <djd15@...>
Date: 2003-08-11T03:24:24+09:00
Subject: Re: Ruby and OOP-design (question of an old "procedural person" ;)

Brian Candler wrote:

>On Mon, Aug 11, 2003 at 02:02:33AM +0900, dblack@superlink.net wrote:
>  
>
>>>Does ruby not have exclusive or? I can't remember at the moment. If it
>>>did, I think the top is the same
>>>as:
>>>
>>>unless a.nil? ^ b.nil?
>>>
>>>Which is still somewhat unclear, I agree.
>>>      
>>>
>>I, however, no long agree with myself :-)  I just forgot about ^.
>>    
>>
>
>However ^ is overloaded, so although it works when comparing false/true with
>false/true, it doesn't with other things; especially since it doubles up as
>a bitwise numeric operator too.
>
>irb(main):001:0> 5 ^ false
>TypeError: cannot convert false into Integer
>        from (irb):1:in `^'
>        from (irb):1
>
>But it does treat 'nil' as 'false'. So you could say:
>
>     if  (a && true) ^ (b && true)
>       ...
>     end
>
>which tests if both a and b are 'true' or both a and b are 'false' in the
>Ruby sense of those terms, but it's still not very pretty. I think it would
>be clearer to write
>
>     if  (a && b) || (!a && !b)
>
>It's not a problem with nil? anyway. If you want to check whether a and b
>are either both zero or both nonzero, you could do
>
>     if (a == 0) == (b == 0)
>       ...
>     end
>  
>
Yeah, I thought of the problem with ^ on the way to lunch.

And I just checked and there's no "xor" equivalent to "and" "or" and 
"not", so you can't work around it
that way.

Perhaps an "xor" keyword (or a ^^ logical xor operator) would be handy 
to have specifically for this
kind of situation, since there's no way to conveniently do (obj1 xor 
obj2) in existance tests.

Then again, I can't think of any places where you'd need to do that.

- Dan