From: seebs@... (Peter Seebach)
Date: 2007-07-28T04:16:28+09:00
Subject: Re: How to pass arguments by reference in a function

In message <0514e8b08bc1a44593d7ffe0ddb5117e@ruby-forum.com>, Lloyd Linklater w
rites:
>That reminds me, in the old days you could do a swap without a third 
>variable using XOR.  e.g.
>
>a = 13
>b = 17
>
>a ^= b
>b ^= a
>a ^= b
>
>and they are swapped.
>
>I know that Ruby might do it as mentioned above.
>
>My question is, which is more efficient?

The xor swap is virtually never more efficient on reasonable hardware.
A casual pass through suggests that, even for the special case of numbers
where a, b, and a^b are all Fixnum-ranged, the straight swap ought to be
noticably faster.

More importantly:  How could doing it that way ever be idiomatic or easy
to understand?  I cannot conceive of a program where I have to swap two
objects quickly, and the need to swap them quickly is so great that a hack
like that would be worth it... and I can't just bypass the swap by improving
the algorithm.

-s