1 files changed, 79 insertions, 0 deletions
diff --git a/vendor/elsa/examples/mutable_arena.rs b/vendor/elsa/examples/mutable_arena.rs
new file mode 100644
index 000000000..d5db2d331
--- /dev/null
+++ b/vendor/elsa/examples/mutable_arena.rs
@@ -0,0 +1,79 @@
+use elsa::FrozenVec;
+
+fn main() {
+    let arena = Arena::new();
+    let lonely = arena.add_person("lonely", vec![]);
+    let best_friend = arena.add_person("best friend", vec![lonely]);
+    let threes_a_crowd = arena.add_person("threes a crowd", vec![lonely, best_friend]);
+    let rando = arena.add_person("rando", vec![]);
+    let _everyone = arena.add_person(
+        "follows everyone",
+        vec![rando, threes_a_crowd, lonely, best_friend],
+    );
+    arena.dump();
+}
+
+struct Arena<'arena> {
+    people: FrozenVec<Box<Person<'arena>>>,
+}
+
+struct Person<'arena> {
+    pub follows: FrozenVec<PersonRef<'arena>>,
+    pub reverse_follows: FrozenVec<PersonRef<'arena>>,
+    pub name: &'static str,
+}
+
+type PersonRef<'arena> = &'arena Person<'arena>;
+
+impl<'arena> Arena<'arena> {
+    fn new() -> Arena<'arena> {
+        Arena {
+            people: FrozenVec::new(),
+        }
+    }
+
+    fn add_person(
+        &'arena self,
+        name: &'static str,
+        follows: Vec<PersonRef<'arena>>,
+    ) -> PersonRef<'arena> {
+        let idx = self.people.len();
+        self.people.push(Box::new(Person {
+            name,
+            follows: follows.into(),
+            reverse_follows: Default::default(),
+        }));
+        let me = &self.people[idx];
+        for friend in &me.follows {
+            friend.reverse_follows.push(me)
+        }
+        me
+    }
+
+    fn dump(&'arena self) {
+        for thing in &self.people {
+            println!("{} network:", thing.name);
+            println!("\tfollowing:");
+            for friend in &thing.follows {
+                println!("\t\t{}", friend.name);
+            }
+            println!("\tfollowers:");
+            for friend in &thing.reverse_follows {
+                println!("\t\t{}", friend.name);
+            }
+        }
+    }
+}
+
+// Note that the following will cause the above code to stop compiling
+// since non-eyepatched custom destructors can potentially
+// read deallocated data.
+//
+// impl<'arena> Drop for Person<'arena> {
+//     fn drop(&mut self) {
+//         println!("goodbye {:?}", self.name);
+//         for friend in &self.follows {
+//             println!("\t\t{}", friend.name);
+//         }
+//     }
+// }