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bevy/examples/ecs/generic_system.rs
Doonv ba0f8f996f
Add insert_state to App. ()
# Objective

Fix .

## Solution

Rename `App::add_state<T>(&mut self)` to `init_state`, and add
`App::insert_state<T>(&mut self, state: T)`. I decided on these names
because they are more similar to `init_resource` and `insert_resource`.

I also removed the `States` trait's requirement for `Default`. Instead,
`init_state` requires `FromWorld`.

---

## Changelog

- Renamed `App::add_state` to `init_state`.
- Added `App::insert_state`.
- Removed the `States` trait's requirement for `Default`.

## Migration Guide

- Renamed `App::add_state` to `init_state`.
2023-12-21 14:09:24 +00:00

89 lines
2.9 KiB
Rust

//! Generic types allow us to reuse logic across many related systems,
//! allowing us to specialize our function's behavior based on which type (or types) are passed in.
//!
//! This is commonly useful for working on related components or resources,
//! where we want to have unique types for querying purposes but want them all to work the same way.
//! This is particularly powerful when combined with user-defined traits to add more functionality to these related types.
//! Remember to insert a specialized copy of the system into the schedule for each type that you want to operate on!
//!
//! For more advice on working with generic types in Rust, check out <https://doc.rust-lang.org/book/ch10-01-syntax.html>
//! or <https://doc.rust-lang.org/rust-by-example/generics.html>
use bevy::prelude::*;
#[derive(Debug, Default, Clone, Copy, Eq, PartialEq, Hash, States)]
enum AppState {
#[default]
MainMenu,
InGame,
}
#[derive(Component)]
struct TextToPrint(String);
#[derive(Component, Deref, DerefMut)]
struct PrinterTick(Timer);
#[derive(Component)]
struct MenuClose;
#[derive(Component)]
struct LevelUnload;
fn main() {
App::new()
.add_plugins(DefaultPlugins)
.init_state::<AppState>()
.add_systems(Startup, setup_system)
.add_systems(
Update,
(
print_text_system,
transition_to_in_game_system.run_if(in_state(AppState::MainMenu)),
),
)
// Cleanup systems.
// Pass in the types your system should operate on using the ::<T> (turbofish) syntax
.add_systems(OnExit(AppState::MainMenu), cleanup_system::<MenuClose>)
.add_systems(OnExit(AppState::InGame), cleanup_system::<LevelUnload>)
.run();
}
fn setup_system(mut commands: Commands) {
commands.spawn((
PrinterTick(Timer::from_seconds(1.0, TimerMode::Repeating)),
TextToPrint("I will print until you press space.".to_string()),
MenuClose,
));
commands.spawn((
PrinterTick(Timer::from_seconds(1.0, TimerMode::Repeating)),
TextToPrint("I will always print".to_string()),
LevelUnload,
));
}
fn print_text_system(time: Res<Time>, mut query: Query<(&mut PrinterTick, &TextToPrint)>) {
for (mut timer, text) in &mut query {
if timer.tick(time.delta()).just_finished() {
info!("{}", text.0);
}
}
}
fn transition_to_in_game_system(
mut next_state: ResMut<NextState<AppState>>,
keyboard_input: Res<ButtonInput<KeyCode>>,
) {
if keyboard_input.pressed(KeyCode::Space) {
next_state.set(AppState::InGame);
}
}
// Type arguments on functions come after the function name, but before ordinary arguments.
// Here, the `Component` trait is a trait bound on T, our generic type
fn cleanup_system<T: Component>(mut commands: Commands, query: Query<Entity, With<T>>) {
for e in &query {
commands.entity(e).despawn_recursive();
}
}