63fee2572b
# Objective Add a system parameter `ParamSet` to be used as container for conflicting parameters. ## Solution Added two methods to the SystemParamState trait, which gives the access used by the parameter. Did the implementation. Added some convenience methods to FilteredAccessSet. Changed `get_conflicts` to return every conflicting component instead of breaking on the first conflicting `FilteredAccess`. Co-authored-by: bilsen <40690317+bilsen@users.noreply.github.com>
2.2 KiB
B0001
To keep Rust rules on references (either one mutable reference or any number of immutable references) on a component, it is not possible to have two queries on the same component when one request mutable access to it in the same system.
Erroneous code example:
use bevy::prelude::*;
#[derive(Component)]
struct Player;
#[derive(Component)]
struct Enemy;
fn move_enemies_to_player(
mut enemies: Query<&mut Transform, With<Enemy>>,
player: Query<&Transform, With<Player>>,
) {
// ...
}
fn main() {
App::new()
.add_plugins(DefaultPlugins)
.add_system(move_enemies_to_player)
.run();
}
This will panic, as it's not possible to have both a mutable and an immutable query on Transform at the same time.
You have two solutions:
Solution #1: use disjoint queries using Without
As a Player entity won't be an Enemy at the same time, those two queries will acutally never target the same entity. This can be encoded in the query filter with Without:
use bevy::prelude::*;
#[derive(Component)]
struct Player;
#[derive(Component)]
struct Enemy;
fn move_enemies_to_player(
mut enemies: Query<&mut Transform, With<Enemy>>,
player: Query<&Transform, (With<Player>, Without<Enemy>)>,
) {
// ...
}
fn main() {
App::new()
.add_plugins(DefaultPlugins)
.add_system(move_enemies_to_player)
.run();
}
Solution #2: use a ParamSet
A ParamSet will let you have conflicting queries as a parameter, but you will still be responsible of not using them at the same time in your system.
use bevy::prelude::*;
#[derive(Component)]
struct Player;
#[derive(Component)]
struct Enemy;
fn move_enemies_to_player(
mut transforms: ParamSet<(
Query<&mut Transform, With<Enemy>>,
Query<&Transform, With<Player>>,
)>,
) {
// ...
}
fn main() {
App::new()
.add_plugins(DefaultPlugins)
.add_system(move_enemies_to_player)
.run();
}