In article <87wsp177pg.fsf / fsij.org>,
  Tanaka Akira <akr / fsij.org> writes:

> Not good idea.
>
> % ./miniruby -ve 'p %r{\}}' 
> ruby 1.8.6 (2008-02-05 patchlevel 5000) [i686-linux]
> -e:1: warning: regexp has `}' without escape
> /}/

More problems:

% ./miniruby -e 'p %r(\))'
-e:1: unmatched ): /)/
% ./miniruby -e 'p %r|\|| =~ "a"'
0
% ./miniruby -e 'p %r?\??'
-e:1: invalid regular expression; there's no previous pattern, to which '?' would define cardinality at 1: /?/

In general, adding/removing a backslash is not safe for
meta characters.

Note that %r%/%.source is "/".  However p %r%/% prints
/\//.  The backslash in /\// is added by Regexp#inspect.  It
is safe because a slash is not a meta character for regexp
engine.
-- 
Tanaka Akira