feat(ecs): add support for singleton components

1 files changed, 71 insertions, 0 deletions

diff --git a/ecs/examples/with_single.rs b/ecs/examples/with_single.rs
new file mode 100644
index 0000000..25b73d1
--- /dev/null
+++ b/ecs/examples/with_single.rs
@@ -0,0 +1,71 @@
+use ecs::component::single::Single;
+use ecs::event::{Event, Id as EventId};
+use ecs::{Component, Query, World};
+
+#[derive(Component)]
+struct Ammo
+{
+    ammo_left: u32,
+}
+
+#[derive(Component, Default)]
+struct AmmoCounter
+{
+    counter: u32,
+}
+
+fn count_ammo(query: Query<(Ammo,)>, mut ammo_counter: Single<AmmoCounter>)
+{
+    for (ammo,) in &query {
+        println!("Found {} ammo", ammo.ammo_left);
+
+        ammo_counter.counter += ammo.ammo_left;
+    }
+}
+
+fn print_total_ammo_count(ammo_counter: Single<AmmoCounter>)
+{
+    println!("Total ammo count: {}", ammo_counter.counter);
+
+    assert_eq!(ammo_counter.counter, 19);
+}
+
+#[derive(Debug)]
+struct EventA;
+
+impl Event for EventA
+{
+    fn id(&self) -> EventId
+    {
+        EventId::of::<Self>()
+    }
+}
+
+#[derive(Debug)]
+struct EventB;
+
+impl Event for EventB
+{
+    fn id(&self) -> EventId
+    {
+        EventId::of::<Self>()
+    }
+}
+
+fn main()
+{
+    let mut world = World::new();
+
+    world.register_system(&EventA, count_ammo);
+    world.register_system(&EventB, print_total_ammo_count);
+
+    world.create_entity((Ammo { ammo_left: 4 },));
+    world.create_entity((Ammo { ammo_left: 7 },));
+    world.create_entity((Ammo { ammo_left: 8 },));
+
+    world.add_single_component(AmmoCounter::default()).unwrap();
+
+    world.emit(&EventA);
+
+    world.emit(&EventB);
+}