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

.gitignore

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+/target

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "rustrefs"
+version = "0.1.0"

Cargo.toml

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+[package]
+name = "rustrefs"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

src/main.rs

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+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();
+}