CHECK {
  my $dp = B::Deparse->new();
  while (my ($pkg, $hash) = each %INTERFACES) {
    while (my ($var, $glob) = each %{"${pkg}::"}) {
      next unless defined &$glob;
      croak "Constructor detected: ${pkg}::$var" if
        $dp->coderef2text(\&{"${pkg}::$var"}) =~ /\bbless\b/;
    }
  }
}