From: Jason Foreman <threeve.org@...>
Date: 2005-06-21T00:17:38+09:00
Subject: Re: x==1 vs 1==x

On 6/20/05, Robert Klemme <bob.news@gmx.net> wrote:
> Jason Foreman wrote:
> > On 6/20/05, Florian Gro� <florgro@gmail.com> wrote:
> >> Jason Foreman wrote:
> >>
> >>> If you accidentally write x = 1 instead of x == 1, it can take a
> >>> long time to figure out your bug.
> >>
> >> C:\Dokumente und Einstellungen\flgr>ruby
> >> foo = 10
> >> if foo = 10 then
> >>    puts "Hello World!"
> >> end
> >> -:2: warning: found = in conditional, should be ==
> >> ^Z
> >> Hello World!
> >>
> >> I found out about my bug before I was even done giving Ruby the full
> >> application code. ;)
> >>
> >>
> >>
> >
> > Nice.  I didn't realize it gave that warning!  :)
> >
> > However:
> >
> > $ ruby
> > x=2
> > case x
> >   when x=1:  p 'one'
> >   when x==2: p 'two'
> >   else p 'whoops!'
> > end
> > ^D
> > "whoops!"
> 
> Do you suggest to add a warning if there is an expression after "case"
> *and* at least a single boolean expression after "when"?  Note that the
> correct form of what you did is this:
> 
> x=2
> case
>   when x==1:  p 'one'
>   when x==2: p 'two'
>   else p 'whoops!'
> end
> 
> Kind regards
> 
>     robert
> 
> 
> 

Right, I should have used "case" and not "case x".  Thanks for
pointing this out.

The corrected example of the problem I was trying to demonstrate is:
$ ruby
x=2
case
  when x=1:  p 'one'
  when x==2: p 'two'
end
^D
"one"


I'm not so sure you could easily add a warning for this, without
crippling some of the capabilities of the language.  Someone may very
well want to do an assignment there.  The probability of someone
writing a case expression like that are probably very low though.

It comes down to the fact that I like to write 1==x, because I made
too many x=1 vs x==1 type of errors when I was learning to program and
now its habit.  Nobody else seems to agree with me though, so whatever
 :)


Jason