lyra-ecs/src/query/borrow.rs

@@ -177,10 +177,10 @@ where
     unsafe fn fetch<'a>(&self, _world: &'a World, archetype: &'a crate::archetype::Archetype, tick: crate::Tick) -> Self::Fetch<'a> {
         let col = archetype.get_column(self.type_id)
             .expect("You ignored 'can_visit_archetype'!");
-        let col = NonNull::from(col);
         
         // TODO: find a way to get the component column mutable with a borrowed archetype so its tick can be updated.
         // the fetcher needs to tick the entities tick in the archetype
+        let col = NonNull::from(col);
 
         FetchBorrowMut {
             col,

lyra-ecs/src/query/filter/has_component.rs

@@ -0,0 +1,40 @@
+use std::marker::PhantomData;
+
+use crate::{query::{AsQuery, Query}, Archetype, Component, DynTypeId, World};
+
+#[derive(Default)]
+pub struct Has<C: Component> {
+    _marker: PhantomData<C>
+}
+
+impl<C: Component> Copy for Has<C> {}
+
+impl<C: Component> Clone for Has<C> {
+    fn clone(&self) -> Self {
+        Self { _marker: self._marker.clone() }
+    }
+}
+
+impl<C: Component> Query for Has<C> {
+    type Item<'a> = ();
+    
+    type Fetch<'a> = ();
+
+    fn new() -> Self {
+        Has {
+            _marker: PhantomData
+        }
+    }
+
+    fn can_visit_archetype(&self, archetype: &Archetype) -> bool {
+        archetype.has_column(DynTypeId::of::<C>())
+    }
+
+    unsafe fn fetch<'a>(&self, _world: &'a World, _: &'a Archetype, _: crate::Tick) -> Self::Fetch<'a> {
+        ()
+    }
+}
+
+impl<C: Component> AsQuery for Has<C> {
+    type Query = Self;
+}

lyra-ecs/src/query/filter/mod.rs

@@ -0,0 +1,5 @@
+pub mod has_component;
+pub use has_component::*;
+
+pub mod or;
+pub use or::*;

lyra-ecs/src/query/filter/or.rs

@@ -0,0 +1,40 @@
+use crate::{query::{AsQuery, Query}, Archetype, World};
+
+#[derive(Default)]
+pub struct Or<Q1: AsQuery, Q2: AsQuery> {
+    left: Q1::Query,
+    right: Q2::Query,
+}
+
+impl<Q1: AsQuery, Q2: AsQuery> Copy for Or<Q1, Q2> {}
+
+impl<Q1: AsQuery, Q2: AsQuery> Clone for Or<Q1, Q2> {
+    fn clone(&self) -> Self {
+        Self { left: self.left.clone(), right: self.right.clone() }
+    }
+}
+
+impl<Q1: AsQuery, Q2: AsQuery> Query for Or<Q1, Q2> {
+    type Item<'a> = ();
+    
+    type Fetch<'a> = ();
+
+    fn new() -> Self {
+        Or {
+            left: Q1::Query::new(),
+            right: Q2::Query::new(),
+        }
+    }
+
+    fn can_visit_archetype(&self, archetype: &Archetype) -> bool {
+        self.left.can_visit_archetype(archetype) || self.right.can_visit_archetype(archetype)
+    }
+
+    unsafe fn fetch<'a>(&self, _world: &'a World, _: &'a Archetype, _: crate::Tick) -> Self::Fetch<'a> {
+        ()
+    }
+}
+
+impl<Q1: AsQuery, Q2: AsQuery> AsQuery for Or<Q1, Q2> {
+    type Query = Self;
+}

lyra-ecs/src/query/mod.rs

@@ -29,6 +29,8 @@ pub use world::*;
 
 pub mod dynamic;
 
+pub mod filter;
+
 /// A [`Fetch`]er implementation gets data out of an archetype.
 pub trait Fetch<'a> {
     /// The type that this Fetch yields

lyra-ecs/src/query/view.rs

@@ -90,7 +90,7 @@ where
 
     fn next(&mut self) -> Option<Self::Item> {
         loop {
-            if Q::ALWAYS_FETCHES && F::ALWAYS_FETCHES {
+            if Q::ALWAYS_FETCHES {
                 // only fetch this query once.
                 // fetcher gets set to Some after this `next` call.
                 if self.fetcher.is_none() {

lyra-ecs/src/world.rs

@@ -254,6 +254,13 @@ impl World {
         v.into_iter()
     }
 
+    /// View into the world for a set of entities that satisfy the queries.
+    pub fn filtered_view_iter<Q: AsQuery, F: AsQuery>(&self) -> ViewIter<Q::Query, F::Query> {
+        let archetypes = self.archetypes.values().collect();
+        let v = ViewState::new(self, Q::Query::new(), F::Query::new(), archetypes);
+        v.into_iter()
+    }
+
     pub fn dynamic_view(&self) -> DynamicView {
         DynamicView::new(self)
     }