From: Lloyd Zusman <ljz@...>
Date: 2005-11-07T12:25:01+09:00
Subject: Re: programming best practices

swille <sillewille@gmail.com> writes:

> [ ... ]
>
> My second question is this.  I occasionally see stuff like
> if -1 == result
>
> rather than
> if result == -1
>
> What, if any, is the benefit of one over the other?
>
> Thanks

Well, the traditional reason is because by putting the number to the
left of the comparison, you're protected against the case where you
might accidentally type a single equal sign instead of a double:

   #!/usr/bin/ruby -W0
   result = 0
   if result = 1     # programmer meant to type "result == 1"
     puts "one"
   else
     puts "not one"
   end

This will print "one", even though "not one" is what is expected.

However, if you do the following, the compiler will give you an
error:

   #!/usr/bin/ruby -W0
   result = 0
   if 1 = result     # programmer meant to type "1 == result"
     puts "one"
   else
     puts "not one"
   end
  
The first case can lead to subtle, very hard to find bugs.  The second
case won't even compile, so you know right away that there's a problem.

Of course, without -W0, you will get a warning in the first case, which
helps you see the potential problem.  Nonetheless, many people have
gotten in the habit of using this little trick, just to be on the safe
side.


-- 
 Lloyd Zusman
 ljz@asfast.com
 God bless you.