The Boids sample is some beautiful code, but, without comments it's a steep learning curve. I watched Mike's presentation and about 30 minutes he lost me. https://www.twitch.tv/videos/242024723?t=29m34s so: Why using hash as index? is there no <vector3, entityIndex> data structure that would do the same? is a hashmap some sort of dictionary where value is a list? do hashmap have set like operations? do hashmap allow querry on one value to get the key? componentgroups have simple set operations, is there intersection as well? any other set like data structure in ECS? When programming in C# I yearn for List.Intersect(OtherList), set theory is sweet like honey. what does SetFilter do? m_BoidGroup.SetFilter(settings); I see mergecell, what is it for? Could we get that same boid example with zero optimization? Seems that a lot of the code is into packing boids in cells and smart tricks in proximity grouping, beautiful stuff, but make things hard to learn.