Observable ECS in C#.

An ECS system that focuses on a clean obserable api surface rather than performance.

Entity

Entity should be an opaque integer type.

Divided into identifer bits and version bits.

C# structs/classes marked with [MessagePackObject] and [Key] attributes for MessagePack-CSharp serialization.

Types must be public — MessagePack requires public accessibility.
Use indexed integer keys ([Key(0)]) for best performance and smallest binary size. String keys are available for debugging/interop but slower.
For contractless usage, [MessagePackObject(keyAsPropertyName: true)] is available.
The MessagePackAnalyzer package provides compile-time validation and AOT-safe source-generated formatters.

Components are stored in sparse-sets so they can cheaply be added/removed.

special components that automanage the source/target.

can be iterated by target for easy reverse lookup.

serializable structs like components, not in ecs but in a queue.

have a run that gets called when you consume the command queue.

a special entity is used to carry singletons.

Queries are composable with With<TComponent> and Without<TComponent> . Iterable for ref TComponent.

Systems are callbacks registered to queries when a tick happens. Ordering of systems is determined at registration time.

ticks can be timed(with deltaTime) or logical(without args).

Use R3 for reactivity api.

Queries can be observed for changes. This is different from iteration for entity/component refs; System always run in ticks and not reactively.

Query subscriptions are not bound to entities but typically bound to, for example, frontend UI lifecycles.

Changes include entity add/remove, or entity component add/remove.

Changes need to be marked and then posted.

When a System makes changes in its run function, changes are posted after the run.

When run happens in a tick, those changes are posted after the tick.

When not in a system run, changes are not posted automatically.

Marking components for updates is manual. structural changes are auto marked.

Entities/Components can be serialized from .csv files or MasterMemory tables.