http://www.perlmonks.org?node_id=665415


in reply to ref() and Regexp

You shouldn't ever have to think about what string ref() returns. By comparing it to a prototype of the same thing, you insulate yourself from version changes and thinkos (like me forgetting if it's REGEX, REGEXP, Regex, or Regexp): 

if( ref $regex eq ref qr// ) { ... }

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Or, hide that in a subroutine is_regex() or something similar.

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brian d foy <brian@stonehenge.com>
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Re^2: ref() and Regexp
by ikegami (Patriarch) on Jan 31, 2008 at 20:02 UTC

    Or, hide that in a subroutine is_regex() or something similar.

    Like this? 

    BEGIN {
   if (!defined(&re::is_regexp)) {
      package re;
      my $re_class = ref qr//;
      *is_regexp = sub($) {
         local *__ANON__ = 'is_regexp';
         return UNIVERSAL::isa($_[0], $re_class);
      };
   }
}

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    Using your philosophy to avoid magical constants, it checks if re::is_regexp is defined rather than checking $] for 5.10.

    BEGIN and the prototype duplicates the behaviour of 5.10's re::is_regexp.

    It uses isa instead of ref so regexes can be made detectable even if there's a need to rebless the regex (by adding Regex to that class's @ISA). It's not an invitation for non-regexes to pretend to be regexes.

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Re^2: ref() and Regexp
by Anonymous Monk on Sep 13, 2009 at 10:37 UTC
    Wouldn't qr/FOO/ be cheaper? (an empty regex is special)
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      an empty regex is special
      In a match (see m//), but not for qr//: 
      $ perl -e 'print qr//;'
(?-xism:)

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