From c29cf44c76e27276011af18789dd70e65621b047 Mon Sep 17 00:00:00 2001
From: Michael Sproul <michael@sigmaprime.io>
Date: Thu, 8 Dec 2022 16:24:15 +1100
Subject: [PATCH] Document historical_batch calculation

---
 consensus/types/src/beacon_state.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/consensus/types/src/beacon_state.rs b/consensus/types/src/beacon_state.rs
index 0583ce83f3..467224ba48 100644
--- a/consensus/types/src/beacon_state.rs
+++ b/consensus/types/src/beacon_state.rs
@@ -473,7 +473,7 @@ impl<T: EthSpec> BeaconState<T> {
     }
 
     pub fn historical_batch(&mut self) -> Result<HistoricalBatch<T>, Error> {
-        // FIXME(sproul): work out how to clean this up (internal mutability?)
+        // Updating before cloning makes the clone cheap and saves repeated hashing.
         self.block_roots_mut().apply_updates()?;
         self.state_roots_mut().apply_updates()?;