I want to write a content based pub/sub system. Where a subscriber says "I want messages where field X = A, y = B and z > C". I've looked around and I've seen

I want to write a content based pub/sub system. Where a subscriber says "I want messages where field X = A, y = B and z > C". I've looked around and I've seen R+ Trees are potentially a solution but there's very little info on how they're actually created in code. Does anyone know of any nice data structures to do this? Obviously the most basic way is just indexing each field and that works for simple equality but gets harder when you're trying to do other comparators like < and >.