What is an Entity Component System?

An Entity Component System or ECS is very similar to a relational database like * SQL*. The [World] is the data store where game objects (also known as [Entity]) live. An [Entity] contains data or [Component]s. The ECS can efficiently query those components.

Give me all entities that have a position and velocity component, and then update the position based on the velocity.

type PosVelQuery = (Write<Pos>, Read<Vel>);
//                  ^^^^^       ^^^^
//                  Mutable     Immutable
world.matcher::<All<PosVelQuery>>().for_each(|(pos, vel)|{
pos += vel;
})

Internals

// A Storage that contains `Pos`, `Vel`, `Health`.
(
[Pos1, Pos2, Pos3, .., PosN],
[Vel1, Vel2, Vel3, .., VelN],
[Health1, Health2, Health3, .., HealthN],
)

// A Storage that contains `Pos`, `Vel`.
(
[Pos1, Pos2, Pos3, .., PosM]
[Vel1, Vel2, Vel3, .., VelM]
)

Iteration is fully linear with the exception of jumping to different storages.

The iteration pattern from the query above would be

positions:  [Pos1, Pos2, Pos3, .., PosN], [Pos1, Pos2, Pos3, .., PosM]
velocities: [Vel1, Vel2, Vel3, .., VelN], [Vel1, Vel2, Vel3, .., VelM]
^
Jump occours here

The jump is something like a chain of two iterators. We look at all the storages that match specific query. If the query would be Write<Position>, then we would look for all the storages that contain a position array, extract the iterators and chain them

Every combination of components will be in a separate storage. This guarantees that iteration will always be linear.

Benchmarks

Getting started