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);
};
}
}
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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