mirror of
https://github.com/bevyengine/bevy
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89cbc78d3d
# Objective Be consistent with `Resource`s and `Components` and have `Event` types be more self-documenting. Although not susceptible to accidentally using a function instead of a value due to `Event`s only being initialized by their type, much of the same reasoning for removing the blanket impl on `Resource` also applies here. * Not immediately obvious if a type is intended to be an event * Prevent invisible conflicts if the same third-party or primitive types are used as events * Allows for further extensions (e.g. opt-in warning for missed events) ## Solution Remove the blanket impl for the `Event` trait. Add a derive macro for it. --- ## Changelog - `Event` is no longer implemented for all applicable types. Add the `#[derive(Event)]` macro for events. ## Migration Guide * Add the `#[derive(Event)]` macro for events. Third-party types used as events should be wrapped in a newtype.
61 lines
2 KiB
Rust
61 lines
2 KiB
Rust
use bevy_ecs::prelude::*;
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// In this example a system sends a custom event with a 50/50 chance during any frame.
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// If an event was send, it will be printed by the console in a receiving system.
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fn main() {
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// Create a new empty world and add the event as a resource
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let mut world = World::new();
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world.insert_resource(Events::<MyEvent>::default());
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// Create a schedule to store our systems
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let mut schedule = Schedule::default();
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// Events need to be updated in every frame in order to clear our buffers.
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// This update should happen before we use the events.
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// Here, we use system sets to control the ordering.
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#[derive(SystemSet, Debug, Clone, PartialEq, Eq, Hash)]
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pub struct FlushEvents;
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schedule.add_systems(Events::<MyEvent>::update_system.in_set(FlushEvents));
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// Add systems sending and receiving events after the events are flushed.
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schedule.add_systems((
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sending_system.after(FlushEvents),
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receiving_system.after(sending_system),
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));
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// Simulate 10 frames of our world
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for iteration in 1..=10 {
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println!("Simulating frame {iteration}/10");
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schedule.run(&mut world);
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}
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}
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// This is our event that we will send and receive in systems
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#[derive(Event)]
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struct MyEvent {
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pub message: String,
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pub random_value: f32,
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}
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// In every frame we will send an event with a 50/50 chance
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fn sending_system(mut event_writer: EventWriter<MyEvent>) {
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let random_value: f32 = rand::random();
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if random_value > 0.5 {
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event_writer.send(MyEvent {
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message: "A random event with value > 0.5".to_string(),
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random_value,
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});
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}
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}
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// This system listens for events of the type MyEvent
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// If an event is received it will be printed to the console
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fn receiving_system(mut event_reader: EventReader<MyEvent>) {
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for my_event in event_reader.iter() {
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println!(
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" Received message {:?}, with random value of {}",
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my_event.message, my_event.random_value
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);
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}
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}
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