wip: closure-based collections

crates/tek_core/src/engine/collect.rs

@@ -54,6 +54,20 @@ impl<'a, E: Engine> Collect<'a, E> for Collection<'a, E> {
 
 pub struct Layers<'a, E: Engine, const N: usize>(pub [&'a dyn Widget<Engine = E>;N]);
 
+pub struct Layers2<
+    E: Engine,
+    F: Send + Sync + Fn(&mut dyn FnMut(&dyn Widget<Engine = E>)->Usually<()>)->Usually<()>
+>(pub F, PhantomData<E>);
+
+impl<
+    E: Engine,
+    F: Send + Sync + Fn(&mut dyn FnMut(&dyn Widget<Engine = E>)->Usually<()>)->Usually<()>
+> Layers2<E, F> {
+    pub fn new (build: F) -> Self {
+        Self(build, Default::default())
+    }
+}
+
 // this actually works, except for the type inference
 //pub struct Layers<'a, E: Engine + 'a, I: std::iter::IntoIterator<Item = &'a dyn Render<E>>>(
     //pub &'a I