class Summary {

	public Summary merge(Summary other) {
		Preconditions.checkNotNull(other);
		
		return Summary.builder()
			.changeCount(changeCount + other.changeCount)
			.deletionCount(deletionCount + other.deletionCount)
			.fetchCount(fetchCount + other.fetchCount)
			.build();
	}

	private  Summary(int changeCount, int deletionCount, int fetchCount);

}