hollow/src/main/java/com/netflix/hollow/api/producer/ReadStateHelper.java
ReadStateHelper swap() {
        return new ReadStateHelper(newReadState(current.getVersion(), pending.getStateEngine()),
                newReadState(pending.getVersion(), current.getStateEngine()));
    }
ReadStateHelper swap() {
        return new ReadStateHelper(newReadState(current.getVersion(), pending.getStateEngine()),
                newReadState(pending.getVersion(), current.getStateEngine()));
    }
Swap underlying state engines between current and pending while keeping the versions consistent;
used after delta integrity checks have altered the underlying state engines.

@return