From: Michael Morin <uzimonkey@...>
Date: 2008-08-31T10:56:49+09:00
Subject: Re: Simple conditional causing hanging?

Will Dresh wrote:
> I have the following conditional inside a method:
> 
> if ( @thisLine.class != 'NilClass' )
>   return @thisLine.class.to_s
> else
>   return 'nope'
> end
> 
> Obviously, all I'm trying to do is test if @thisLine is nil or not.
> When I call this method later on from inside the program, at a point
> when I know that @thisLine is nil, it returns 'NilClass'.  This means
> that my conditional has failed; it should have returned 'nope'.
> 
> Alright, this makes sense to me.  It's failing because I'm trying to
> compare an object of type Class (@thisLine.class) to an object of type
> String ('NilClass').  Easy fix, right?  I'll just convert that Class
> object to a String object before comparing...
> 
> if ( @thisLine.class.to_s != 'NilClass' )
>   return @thisLine.class.to_s
> else
>   return 'nope'
> end
> 
> But now, when I call this method, my program hangs.  I am completely
> stumped as to why this happens.  Any variations to this that I think
> WOULD work properly, also hang.  In addition to the above code, I have
> also tried:
> 
> if ( @thisLine != nil )
> if ( @thisLine.class != NilClass )
> 
> I would very much appreciate it if someone could explain to me why these
> extremely simple method calls are apparently causing the program to
> hang.
> 
> Thanks!
> -Will

You want @thisLine.nil?.  Alternatively, you could use @thisLine == nil, 
@thisLine.class == NilClass, or even @thisClass === NilClass.  But 
@thisLine.nil? is the preferred way.

-- 
Michael Morin
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