I think ref($check_re) ne 'Regexp' can fail in modern Perls. You want to use 

use re qw( is_regexp );
is_regexp($check_re)

[download]
Or if you want to support Perl < 5.10, 
BEGIN {
   eval 'use re qw( is_regexp )';
   if (!defined(&is_regexp)) {
      my $re_class = ref qr//;
      *is_regexp = sub($) {
         local *__ANON__ = 'is_regexp';
         return UNIVERSAL::isa($_[0], $re_class);
      };
   }
}

is_regexp($check_re)

[download]

That said, I don't think you should be checking if it's a compiled regex pattern at all. Just checking if it looks like one (as I did) is much more tolerant.

In reply to Re^2: Get regexp modifiers by ikegami
in thread Get regexp modifiers by KSURi

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