From 7269a884c91d539c6e6ec275a6d9ef6d6bd5f142 Mon Sep 17 00:00:00 2001
From: Oliver Scherer <github35764891676564198441@oli-obk.de>
Date: Tue, 22 Jan 2019 16:46:05 +0100
Subject: [PATCH 1/2] Expose `AllocId`s for priroda

---
 src/mono_hash_map.rs | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/mono_hash_map.rs b/src/mono_hash_map.rs
index 278bbd9cf2b1..56d6e1400f3e 100644
--- a/src/mono_hash_map.rs
+++ b/src/mono_hash_map.rs
@@ -18,8 +18,11 @@ use crate::AllocMap;
 pub struct MonoHashMap<K: Hash + Eq, V>(RefCell<FxHashMap<K, Box<V>>>);
 
 impl<K: Hash + Eq, V> MonoHashMap<K, V> {
-    pub fn values<T>(&self, f: impl FnOnce(&mut dyn Iterator<Item=&V>) -> T) -> T {
-        f(&mut self.0.borrow().values().map(|v| &**v))
+    /// This function exists for priroda to be able to iterate over all evaluator memory
+    ///
+    /// The memory of constants does not show up in this list.
+    pub fn iter<T>(&self, f: impl FnOnce(&mut dyn Iterator<Item=(&K, &V)>) -> T) -> T {
+        f(&mut self.0.borrow().iter().map(|(k, v)| (k, &**v)))
     }
 }
 

From 9f06cdc87a450b486a5bfea209acf958de92dfc8 Mon Sep 17 00:00:00 2001
From: Oliver Scherer <github35764891676564198441@oli-obk.de>
Date: Tue, 22 Jan 2019 17:19:19 +0100
Subject: [PATCH 2/2] Explain Ref problems

---
 src/mono_hash_map.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/mono_hash_map.rs b/src/mono_hash_map.rs
index 56d6e1400f3e..ec1a5fdb4288 100644
--- a/src/mono_hash_map.rs
+++ b/src/mono_hash_map.rs
@@ -20,7 +20,12 @@ pub struct MonoHashMap<K: Hash + Eq, V>(RefCell<FxHashMap<K, Box<V>>>);
 impl<K: Hash + Eq, V> MonoHashMap<K, V> {
     /// This function exists for priroda to be able to iterate over all evaluator memory
     ///
-    /// The memory of constants does not show up in this list.
+    /// The function is somewhat roundabout with the closure argument because internally the
+    /// `MonoHashMap` uses a `RefCell`. When iterating over the `HashMap` inside the `RefCell`,
+    /// we need to keep a borrow to the `HashMap` inside the iterator. The borrow is only alive
+    /// as long as the `Ref` returned by `RefCell::borrow()` is alive. So we can't return the
+    /// iterator, as that would drop the `Ref`. We can't return both, as it's not possible in Rust
+    /// to have a struct/tuple with a field that refers to another field.
     pub fn iter<T>(&self, f: impl FnOnce(&mut dyn Iterator<Item=(&K, &V)>) -> T) -> T {
         f(&mut self.0.borrow().iter().map(|(k, v)| (k, &**v)))
     }