sub _rebuild_cache {
    my ($pkg, $exports, $cache) = @_;
    s/^&// foreach @$exports;
    @{$cache}{@$exports} = (1) x @$exports;
    my $ok = \@{"${pkg}::EXPORT_OK"};
    if (@$ok) {
	s/^&// foreach @$ok;
	@{$cache}{@$ok} = (1) x @$ok;
    }
}