You don't need a readonly hash if you just use a closure...no code outside the block can change the hash:
BEGIN {
  my %members;
  undef @members{qw(age old years)};
  sub is_member {
    return exists $members{$_[0]};
  }
}

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In reply to Re: Fastest way to test membership in a constant set by runrig
in thread Fastest way to test membership in a constant set by Anonymous Monk

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