1 files changed, 56 insertions, 0 deletions
diff --git a/ecs/src/extension.rs b/ecs/src/extension.rs
new file mode 100644
index 0000000..fc5a345
--- /dev/null
+++ b/ecs/src/extension.rs
@@ -0,0 +1,56 @@
+use crate::component::Sequence as ComponentSequence;
+use crate::event::Event;
+use crate::sole::Sole;
+use crate::system::System;
+use crate::{SoleAlreadyExistsError, World};
+
+/// A collection of systems, entities & soles that can be added to a [`World`].
+pub trait Extension
+{
+    fn collect(self, collector: Collector<'_>);
+}
+
+/// Passed to a [`Extension`] to collects it's systems, entities & soles.
+pub struct Collector<'world>
+{
+    world: &'world mut World,
+}
+
+impl<'world> Collector<'world>
+{
+    /// Returns a new `Collector` for the given [`World`].
+    pub fn new(world: &'world mut World) -> Self
+    {
+        Self { world }
+    }
+
+    /// Adds a system to the [`World`].
+    pub fn add_system<'this, EventT, SystemImpl>(
+        &'this mut self,
+        event: EventT,
+        system: impl System<'this, SystemImpl>,
+    ) where
+        EventT: Event,
+    {
+        self.world.register_system(event, system);
+    }
+
+    /// Adds a entity to the [`World`].
+    pub fn add_entity<Comps>(&mut self, components: Comps)
+    where
+        Comps: ComponentSequence,
+    {
+        self.world.create_entity(components);
+    }
+
+    /// Adds a globally shared singleton value to the [`World`].
+    ///
+    /// # Errors
+    /// Returns `Err` if this [`Sole`] has already been added.
+    pub fn add_sole<SoleT>(&mut self, sole: SoleT) -> Result<(), SoleAlreadyExistsError>
+    where
+        SoleT: Sole,
+    {
+        self.world.add_sole(sole)
+    }
+}