add app builder shorthand for system function

crates/bevy_app/src/app_builder.rs

@@ -4,7 +4,9 @@ use crate::{
     stage, App, AppExit, Events,
 };
 
-use legion::prelude::{Resources, Universe, World};
+use legion::prelude::{Resources, Universe, World, IntoQuery, ResourceSet, into_system, into_resource_system};
+use legion::query::{View, DefaultFilter};
+use legion::filter::EntityFilter;
 
 static APP_MISSING_MESSAGE: &str = "This AppBuilder no longer has an App. Check to see if you already called run(). A call to app_builder.run() consumes the AppBuilder's App.";
 
@@ -237,4 +239,46 @@ impl AppBuilder {
         plugin.build(self);
         self
     }
+
+    pub fn add_system_fn<'a, Q, F, R, X>(&mut self, name: &'static str, system: F) -> &mut Self
+    where
+        Q: IntoQuery + DefaultFilter<Filter = R>,
+        <Q as View<'a>>::Iter: Iterator<Item = Q> + 'a,
+        F: FnMut(&mut X, Q) + Send + Sync + 'static,
+        R: EntityFilter + Sync + 'static,
+        X: ResourceSet<PreparedResources = X> + 'static,
+    {
+        self.add_system_fn_to_stage(stage::UPDATE, name, system)
+    }
+
+    pub fn add_system_fn_to_stage<'a, Q, F, R, X>(&mut self, stage_name: &str, name: &'static str, system: F) -> &mut Self
+    where
+        Q: IntoQuery + DefaultFilter<Filter = R>,
+        <Q as View<'a>>::Iter: Iterator<Item = Q> + 'a,
+        F: FnMut(&mut X, Q) + Send + Sync + 'static,
+        R: EntityFilter + Sync + 'static,
+        X: ResourceSet<PreparedResources = X> + 'static,
+    {
+        let system = into_system(name, system);
+        self.add_system_to_stage(stage_name, system);
+        self
+    }
+
+    pub fn add_resource_system_fn<'a, F, X>(&mut self, name: &'static str, system: F) -> &mut Self
+    where
+        F: FnMut(&mut X) + Send + Sync + 'static,
+        X: ResourceSet<PreparedResources = X> + 'static,
+    {
+        self.add_resource_system_fn_to_stage(stage::UPDATE, name, system)
+    }
+
+    pub fn add_resource_system_fn_to_stage<'a, F, X>(&mut self, stage_name: &str, name: &'static str, system: F) -> &mut Self
+    where
+        F: FnMut(&mut X) + Send + Sync + 'static,
+        X: ResourceSet<PreparedResources = X> + 'static,
+    {
+        let system = into_resource_system(name, system);
+        self.add_system_to_stage(stage_name, system);
+        self
+    }
 }

examples/event.rs

@@ -6,11 +6,8 @@ fn main() {
         .add_event::<MyEvent>()
         .add_resource(EventTriggerState::default())
         .add_resource_init::<EventListenerState>()
-        .add_system(into_resource_system("event_trigger", event_trigger_system))
-        .add_system(into_resource_system(
-            "event_listener",
-            event_listener_system,
-        ))
+        .add_resource_system_fn("event_trigger", event_trigger_system)
+        .add_resource_system_fn("event_listener", event_listener_system)
         .run();
 }
 

examples/spawner.rs

@@ -9,7 +9,7 @@ fn main() {
             ..Default::default()
         })
         .add_startup_system(setup)
-        .add_system(into_system("move", move_system))
+        .add_system_fn("move", move_system)
         .run();
 }