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Example

use specs::prelude::*;// A component contains data// which is associated with an entity.#[derive(Debug)]structVel(f32);implComponentforVel{typeStorage =VecStorage<Self>;}#[derive(Debug)]structPos(f32);implComponentforPos{typeStorage =VecStorage<Self>;}structSysA;impl<'a>System<'a>forSysA{// These are the resources required for execution.// You can also define a struct and `#[derive(SystemData)]`,// see the `full` example.typeSystemData =(WriteStorage<'a,Pos>,ReadStorage<'a,Vel>);fnrun(&mutself,(mut pos, vel):Self::SystemData){// The `.join()` combines multiple component storages,// so we get access to all entities which have// both a position and a velocity.for(pos, vel)in(&mut pos,&vel).join(){            pos.0 += vel.0;}}}fnmain(){// The `World` is our// container for components// and other resources.letmut world =World::new();    world.register::<Pos>();    world.register::<Vel>();// An entity may or may not contain some component.    world.create_entity().with(Vel(2.0)).with(Pos(0.0)).build();    world.create_entity().with(Vel(4.0)).with(Pos(1.6)).build();    world.create_entity().with(Vel(1.5)).with(Pos(5.4)).build();// This entity does not have `Vel`, so it won't be dispatched.    world.create_entity().with(Pos(2.0)).build();// This builds a dispatcher.// The third parameter of `with` specifies// logical dependencies on other systems.// Since we only have one, we don't depend on anything.// See the `full` example for dependencies.letmut dispatcher =DispatcherBuilder::new().with(SysA,"sys_a",&[]).build();// This will call the `setup` function of every system.// In this example this has no effect since we already registered our components.    dispatcher.setup(&mut world);// This dispatches all the systems in parallel (but blocking).    dispatcher.dispatch(&mut world);}

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