in reply to
Re^3: Character class in an array
in thread Character class in an array
I was just extending the original poster's qr/// suggestion. If you interpolate a variable in a 'qr' string, it "stays" interpolated and will not change if the value of the original variable changes with it, unless you re-create the string for every iteration.
Obviously, if you're going to want to use qr/// or the /o flag on a regex, you are doing so because you wish Perl to compile the regular expression once (at least within the lexical scope of the qr/// string).