[Feature Request] Single-tick components

[MelonHell]

It would be really great to see support for single-tick components.
They’re very useful for passing events from one system to another.

[Quillraven]

What is a single tick component? Never heard that before. Can you explain it please or describe what you are trying to achieve?

[MelonHell]

A type of components that are automatically removed at the end of the tick.
This could be implemented either as a flag in the Component interface:

interface Component<T> {
    fun type(): ComponentType<T>
    fun World.onAdd(entity: Entity) = Unit
    fun World.onRemove(entity: Entity) = Unit
    fun shouldRemoveOnTickEnd(): Boolean = false
}

or as a separate interface:

interface EventComponent<T> : Component<T>

Here are a few usage examples:

• The input reading system writes an InputEventComponent to entities; the movement system and jump system read those components; at the end of the tick they are automatically removed.
• The physics system adds a CollisionEventComponent when objects collide, and other systems can use that event to play sounds or trigger visual effects.

[Quillraven]

Interesting idea but I am not sure that this should be included in Fleks directly. To me this sounds like a specific architectural decision in your game.

E.g. I always used an "event system" for the things you just mentioned like firing an input event and then systems can react to it and do what they need to do. There are no components involved.

Also, you can already solve your problem by just creating a "CleanupSystem" that has a family with "any" of the components you want to remove. Register it as last/first system and remove the components in there.

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That being said I like the idea and that you get a purely "ECS driven" approach for event handling. Unfortunately, I don't have time at the moment and near future to work on such features but if you are motivated feel free to create a PR for it. I do have time for reviews 😊

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edit: one solution might be also a cleanup system as described above that is provided by Fleks and can be enabled in configureWorld. That way we don't need to adjust any interfaces or introduce new things and just work with existing functionality.