feat(ecs): add read-only query iterating

1 files changed, 69 insertions, 6 deletions

diff --git a/ecs/src/system.rs b/ecs/src/system.rs
index 7c0e454..afb5aac 100644
--- a/ecs/src/system.rs
+++ b/ecs/src/system.rs
@@ -7,8 +7,12 @@ use std::panic::{RefUnwindSafe, UnwindSafe};
 
 use seq_macro::seq;
 
-use crate::component::{Component, FromOptional as FromOptionalComponent};
-use crate::lock::WriteGuard;
+use crate::component::{
+    Component,
+    FromOptional as FromOptionalComponent,
+    FromOptionalMut as FromOptionalMutComponent,
+};
+use crate::lock::{ReadGuard, WriteGuard};
 use crate::system::util::check_params_are_compatible;
 use crate::tuple::{ReduceElement as TupleReduceElement, With as TupleWith};
 use crate::World;
@@ -214,10 +218,10 @@ impl<'a, ComponentT: Component> ComponentRefMut<'a, ComponentT>
     }
 }
 
-impl<'component, ComponentT: Component> FromOptionalComponent<'component>
+impl<'component, ComponentT: Component> FromOptionalMutComponent<'component>
     for ComponentRefMut<'component, ComponentT>
 {
-    fn from_optional_component(
+    fn from_optional_mut_component(
         inner: Option<WriteGuard<'component, Box<dyn Component>>>,
         _world: &'component World,
     ) -> Self
@@ -234,12 +238,12 @@ impl<'component, ComponentT: Component> FromOptionalComponent<'component>
     }
 }
 
-impl<'comp, ComponentT> FromOptionalComponent<'comp>
+impl<'comp, ComponentT> FromOptionalMutComponent<'comp>
     for Option<ComponentRefMut<'comp, ComponentT>>
 where
     ComponentT: Component,
 {
-    fn from_optional_component(
+    fn from_optional_mut_component(
         optional_component: Option<WriteGuard<'comp, Box<dyn Component>>>,
         _world: &'comp World,
     ) -> Self
@@ -265,3 +269,62 @@ impl<'a, ComponentT: Component> DerefMut for ComponentRefMut<'a, ComponentT>
         self.inner.downcast_mut().unwrap()
     }
 }
+
+#[derive(Debug)]
+pub struct ComponentRef<'a, ComponentT: Component>
+{
+    inner: ReadGuard<'a, Box<dyn Component>>,
+    _ph: PhantomData<ComponentT>,
+}
+
+impl<'a, ComponentT: Component> ComponentRef<'a, ComponentT>
+{
+    pub(crate) fn new(inner: ReadGuard<'a, Box<dyn Component>>) -> Self
+    {
+        Self { inner, _ph: PhantomData }
+    }
+}
+
+impl<'component, ComponentT: Component> FromOptionalComponent<'component>
+    for ComponentRef<'component, ComponentT>
+{
+    fn from_optional_component(
+        inner: Option<ReadGuard<'component, Box<dyn Component>>>,
+        _world: &'component World,
+    ) -> Self
+    {
+        Self {
+            inner: inner.unwrap_or_else(|| {
+                panic!(
+                    "Component {} was not found in entity",
+                    type_name::<ComponentT>()
+                );
+            }),
+            _ph: PhantomData,
+        }
+    }
+}
+
+impl<'comp, ComponentT> FromOptionalComponent<'comp>
+    for Option<ComponentRef<'comp, ComponentT>>
+where
+    ComponentT: Component,
+{
+    fn from_optional_component(
+        optional_component: Option<ReadGuard<'comp, Box<dyn Component>>>,
+        _world: &'comp World,
+    ) -> Self
+    {
+        optional_component.map(|component| ComponentRef::new(component))
+    }
+}
+
+impl<'a, ComponentT: Component> Deref for ComponentRef<'a, ComponentT>
+{
+    type Target = ComponentT;
+
+    fn deref(&self) -> &Self::Target
+    {
+        self.inner.downcast_ref().unwrap()
+    }
+}