--- title: Delegates order: 5 description: 'Delegate signatures for fennecs Stream runners - ComponentAction, EntityComponentAction, and MemoryAction, with uniform variants for passing data in.' --- # Delegates Runner methods on Steam Queries expect delegates (Actions) to call. The delegate signatures mirror the count and order of the Query's Stream Types. ## `ComponentAction<>` and `UniformComponentAction<>` These are invoked by [`Stream<>.For`](Stream.For.md) and [`Stream<>.Job`](Stream.Job.md). The Uniforms are contravariant, which helps with code reuse when you refactor your anonymous, named, or static method signatures to take broader data types. ::: code-group ```cs [basic] delegate void ComponentAction(ref C0 comp0); delegate void ComponentAction(ref C0 comp0, ref C1 comp1); delegate void ComponentAction(ref C0 comp0, ref C1 comp1, ref C2 comp2); delegate void ComponentAction(ref C0 comp0, ref C1 comp1, ref C2 comp2, ref C3 comp3); delegate void ComponentAction(ref C0 comp0, ref C1 comp1, ref C2 comp2, ref C3 comp3, ref C4 comp4); ``` ```cs [with uniform] delegate void UniformComponentAction(U uniform, ref C0 comp0); delegate void UniformComponentAction(U uniform, ref C0 comp0, ref C1 comp1); delegate void UniformComponentAction(U uniform, ref C0 comp0, ref C1 comp1, ref C2 comp2); delegate void UniformComponentAction(U uniform, ref C0 comp0, ref C1 comp1, ref C2 comp2, ref C3 comp3); delegate void UniformComponentAction(U uniform, ref C0 comp0, ref C1 comp1, ref C2 comp2, ref C3 comp3, ref C4 comp4); ``` ::: ## `EntityComponentAction<>` and `UniformEntityComponentAction<>` These are invokable through [`Stream<>.For`](Stream.For.md). In addition to the Components and optional Uniform, they also receive an `EntityRef` that can be used to interact structurally with the Entity right then and there (structural changes are deferred until the Runner completes). `EntityRef` is a `ref struct` and cannot leave the delegate's scope – to keep a handle around, store its `Entity` property (or rely on the implicit conversion to `Entity`). ::: code-group ```cs [basic] delegate void EntityComponentAction(in EntityRef entity, ref C0 comp0); delegate void EntityComponentAction(in EntityRef entity, ref C0 comp0, ref C1 comp1); delegate void EntityComponentAction(in EntityRef entity, ref C0 comp0, ref C1 comp1, ref C2 comp2); delegate void EntityComponentAction(in EntityRef entity, ref C0 comp0, ref C1 comp1, ref C2 comp2, ref C3 comp3); delegate void EntityComponentAction(in EntityRef entity, ref C0 comp0, ref C1 comp1, ref C2 comp2, ref C3 comp3, ref C4 comp4); ``` ```cs [with uniform] delegate void UniformEntityComponentAction(U uniform, in EntityRef entity, ref C0 comp0); delegate void UniformEntityComponentAction(U uniform, in EntityRef entity, ref C0 comp0, ref C1 comp1); delegate void UniformEntityComponentAction(U uniform, in EntityRef entity, ref C0 comp0, ref C1 comp1, ref C2 comp2); delegate void UniformEntityComponentAction(U uniform, in EntityRef entity, ref C0 comp0, ref C1 comp1, ref C2 comp2, ref C3 comp3); delegate void UniformEntityComponentAction(U uniform, in EntityRef entity, ref C0 comp0, ref C1 comp1, ref C2 comp2, ref C3 comp3, ref C4 comp4); ``` ::: ## `MemoryAction<>` and `MemoryUniformAction<>` These are invoked by [`Stream<>.Raw`](Stream.Raw.md). ::: code-group ```cs [basic] delegate void MemoryAction(Memory comp0); delegate void MemoryAction(Memory comp0, Memory comp1); delegate void MemoryAction(Memory comp0, Memory comp1, Memory comp2); delegate void MemoryAction(Memory comp0, Memory comp1, Memory comp2, Memory comp3); delegate void MemoryAction(Memory comp0, Memory comp1, Memory comp2, Memory comp3, Memory comp4); ``` ```cs [with uniform] delegate void MemoryUniformAction(U uniform, Memory comp0); delegate void MemoryUniformAction(U uniform, Memory comp0, Memory comp1); delegate void MemoryUniformAction(U uniform, Memory comp0, Memory comp1, Memory comp2); delegate void MemoryUniformAction(U uniform, Memory comp0, Memory comp1, Memory comp2, Memory comp3); delegate void MemoryUniformAction(U uniform, Memory comp0, Memory comp1, Memory comp2, Memory comp3, Memory comp4); ``` ::: ## My name is `in`-igo Montoya ::: warning *"You keep using that keyword. I do not think it means what you think it means."* The `in` keyword in the `Uniform*` delegates' type parmeters denotes [contravariance](https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/covariance-contravariance/). This simply means that the `U` parameter can be a broader type than the one you pass in. It does not mean `readonly` or `in` as in C# method arguments, but uniforms are still always passed by value. If that value is a reference type, you can of course do [fun stuff](/cookbook/staples/Numbering.md) with it... 🦊 Components are always passed by reference because they reside in a special storage object that enables this. ::: Attentive readers will notice that reference type Uniforms passed to a `Job` should, of course, be chosen carefully to be thread safe if they are to be mutated from multiple threads. Anything in `System.Collections.Concurrent` is a faithful friend here. ## Uniforms Uniforms are a way to pass data to your `For`, `Job`, and even `Raw` delegates. They are passed by value, and can be of any type. They are neat to feed data to your delegates that is not part of the component data, but relevant to the operation you are performing. Typical examples of uniforms are the current dt (delta time) or positions or forces, e.g. for explosions or swarming behaviour, or even a list of UI objects that were clicked. ## Varyings Later versions of **fenn**ecs may introduce the concept of "varyings". If you need this feature, please don't hesitate to reach out with some ideas and use cases! ### Varyings at Home Until then, you can use a mutable reference type object as a uniform, and pass it to your `For` or `Job` delegate. This way, you can mutate the object from the delegate, and each subsequent calls will see these changes. ### Remember: Thread fast, thread hard, and thread safe! But alas, where many threads live, there also be dragons. :neofox_hug_dragn_heart: