pebble/ecs/
observers.rs

1use crate::ecs::{resources::Resources, system_param::SystemParam};
2
3/// An observer's first parameter — the event that triggered it. Derefs
4/// straight to `E`, so `trigger.some_field` reads directly through.
5pub struct Trigger<'a, E> {
6    event: &'a E,
7}
8
9impl<'a, E> std::ops::Deref for Trigger<'a, E> {
10    type Target = E;
11
12    fn deref(&self) -> &E {
13        self.event
14    }
15}
16
17/// A runnable observer — the type-erased form `IntoObserverSystem` produces.
18pub trait ObserverSystem<E>: 'static {
19    fn run(&mut self, event: &E, world: &hecs::World, resources: &Resources);
20}
21
22/// Wraps a plain observer function, holding its parameters' state between calls.
23pub struct FunctionObserver<F, E, Marker, State = ()> {
24    func: F,
25    state: State,
26    _marker: std::marker::PhantomData<(E, Marker)>,
27}
28
29/// Implemented for any function shaped `fn(Trigger<E>, ...other params)` —
30/// what lets a plain function be passed directly to `App::add_observer`.
31pub trait IntoObserverSystem<E, Marker> {
32    type System: ObserverSystem<E>;
33
34    fn into_observer_system(self) -> Self::System;
35}
36
37macro_rules! impl_observer_system {
38    ($($param:ident),*) => {
39        impl<T, Evt: 'static, $($param),*> IntoObserverSystem<Evt, ($($param,)*)> for T
40        where
41            T: FnMut(Trigger<Evt>, $($param),*) + for<'a> FnMut(Trigger<'a, Evt>, $($param::Item<'a>),*) + 'static,
42            $($param: SystemParam + 'static),*
43        {
44            type System = FunctionObserver<T, Evt, ($($param,)*), ($($param::State,)*)>;
45            fn into_observer_system(self) -> Self::System {
46                FunctionObserver {
47                    func: self,
48                    state: Default::default(),
49                    _marker: std::marker::PhantomData,
50                }
51            }
52        }
53        impl<T, Evt: 'static, $($param),*> ObserverSystem<Evt> for FunctionObserver<T, Evt, ($($param,)*), ($($param::State,)*)>
54        where
55            T: FnMut(Trigger<Evt>, $($param),*) + for<'a> FnMut(Trigger<'a, Evt>, $($param::Item<'a>),*) + 'static,
56            $($param: SystemParam + 'static),*
57        {
58            fn run(&mut self, _event: &Evt, _world: &hecs::World, _resources: &Resources) {
59                let trigger = Trigger { event: _event };
60                #[allow(non_snake_case)]
61                let ($($param,)*) = &mut self.state;
62                (self.func)(trigger, $($param::fetch(_world, _resources, $param)),*);
63            }
64        }
65    };
66}
67
68impl_observer_system!();
69impl_observer_system!(A);
70impl_observer_system!(A, B);
71impl_observer_system!(A, B, C);
72impl_observer_system!(A, B, C, D);
73impl_observer_system!(A, B, C, D, E);
74impl_observer_system!(A, B, C, D, E, F);
75impl_observer_system!(A, B, C, D, E, F, G);
76impl_observer_system!(A, B, C, D, E, F, G, H);
77impl_observer_system!(A, B, C, D, E, F, G, H, I);
78impl_observer_system!(A, B, C, D, E, F, G, H, I, J);
79impl_observer_system!(A, B, C, D, E, F, G, H, I, J, K);
80impl_observer_system!(A, B, C, D, E, F, G, H, I, J, K, L);
81
82pub(crate) struct Observers<E>(pub(crate) Vec<Box<dyn ObserverSystem<E>>>);
83
84impl<E> Default for Observers<E> {
85    fn default() -> Self {
86        Self(Vec::new())
87    }
88}
pebble/ecs/observers.rs

pebble/ecs/
observers.rs
