return expensiveFlatten(flattenType, maybeFilter(specs, ignoreSpec, filtered), size);
    }

    private FlattenOperationResult filterOnly(Set<ExcludeSpec> specs, Predicate<ExcludeSpec> ignoreSpec) {
        return FlattenOperationResult.of(specs.stream().filter(e -> !ignoreSpec.test(e)).collect(toSet()));
    }