Test to understand how to refer to things sharing a lifetime.

src/main.rs

@@ -0,0 +1,33 @@
+use std::collections::HashMap;
+
+trait Material {}
+struct Impl1 {}
+impl Material for Impl1 {}
+
+trait Shape {}
+struct Impl2<M: Material> {
+    v: M,
+}
+impl<M> Shape for Impl2<M> where M: Material {}
+impl Material for &Box<dyn Material> {}
+
+struct State {
+    materials: HashMap<String, Box<dyn Material>>,
+    shape: Box<dyn Shape>,
+}
+
+fn load_map() -> State {
+    let mut materials: HashMap<String, Box<dyn Material>> = HashMap::new();
+    materials.insert("one".to_string(), Box::new(Impl1 {}));
+    materials.insert("two".to_string(), Box::new(Impl1 {}));
+
+    let shape = Box::new(Impl2 {
+        v: materials.get("one").unwrap(),
+    });
+
+    State { materials, shape }
+}
+
+fn main() {
+    let _ = load_map();
+}