class StructRegistry {

    Iterator<StructSpec> commonStructs() {
        return new Iterator<StructSpec>() {
            private final Iterator<String> iter = commonStructNames.iterator();

            @Override
            public boolean hasNext() {
                return iter.hasNext();
            }

            @Override
            public StructSpec next() {
                return structs.get(iter.next()).spec;
            }
        };
    }

      StructRegistry();

}