From: Caleb Clausen <caleb@...>
Date: 2008-09-25T03:56:03+09:00
Subject: [ruby-core:18865] Re: tokenizing regular expressions when passed as method params

Seth Dillingham wrote:
> If the method call is parenthesized, there's no problem:
> 
>   foo.bar( /regex/, bat )
> 
> If the regular expression is not the first parameter, there's no problem:
> 
>   foo.bar bat, /regex/
> 
> However, if there are no parentheses and the regular expression is the
> first parameter, there is definitely a problem:
> 
>   foo.bar /regex/, bat
> 
> I can't figure out how to tell if that '/' is dividing foo.bar by
> whatever comes next, or if it's a regular expression.

Cases like this are mostly resolved by what I call the before but not 
after rule. If there is whitespace before, but not after the ambiguous 
character(s), (and a method call before the whitespace), then the 
ambiguous character(s) are considered to start a value (in this case a 
regex) rather than an operator.

in short:
foo/bar   #operator
foo /bar/ #regexp
foo/ bar  #operator
foo / bar #operator

I inferred this rule by playing around in irb; (unlike Ryan I am 
incapable of understanding the output of 'ruby -y'), so there may be 
more to it than that... in fact there seems to be an exception, which I 
posted about relatively recently (see [ruby-core:18555]). (I'm unhappy 
about this exception, as it makes no sense to me. But I got no replies, 
so maybe no-one else cares.)