From: Mark Hubbart <discordantus@...>
Date: 2005-09-02T00:26:29+09:00
Subject: Re: palindrome finder

On 9/1/05, Berger, Daniel <Daniel.Berger@qwest.com> wrote:
> > -----Original Message-----
> > From: Josh Charles [mailto:josh.charles@gmail.com]
> > Sent: Thursday, September 01, 2005 9:06 AM
> > To: ruby-talk ML
> > Subject: palindrome finder
> >
> >
> > I've been working on this piece of code and it's starting to
> > drive me crazy.  I think it's a problem with reference vs
> > value type, but I'm not sure.  I'm just writing a simple
> > program to process a list of words and print out all the
> > palindromes (words that read the same forward and backward)
> >
> > Here is my code:
> >
> > file = File.open("testdict.txt", "r" ) do |file|
> >     file.each_line("\n") do |line|
> >         #filelist.push( line )
> >         line.downcase!
> >         if (line == line.reverse)
> >             puts line
> >         end
> >     end
> > end
> >
> > I've made sure each line is being read properly, and it is.
> > The if statement never returns true, however.  I'm new to
> > ruby, so I'm probably just doing something really stupid, but
> > I can't figure it out yet.
> 
> That can be shortened to:
> 
> IO.foreach("testdict.txt"){ |line|
>     line.downcase!.chomp!
>     puts line if line == line.reverse?
> }
> 
> Note the chomp!

Beware of the bang methods. They can be dangerous when chained:

  a="test\n"  
    ==>"test\n"
  a.downcase!.chomp!
  NoMethodError: private method `chomp!' called for nil:NilClass
        from (irb):50
  a
    ==>"test\n"

instead, use:
  line=line.downcase.chomp
or
  line = line.downcase.strip
... which will remove *all* surrounding whitespace, not just newlines.

cheers,
Mark