From 006c194d00d048a873beccbf3d7c01950a6f22ab Mon Sep 17 00:00:00 2001
From: Michael Davis <mcarsondavis@gmail.com>
Date: Thu, 19 Sep 2024 11:10:07 -0400
Subject: [PATCH] dedups: prefer maps:fold/3 to maps:filter/2

---
 src/khepri_machine.erl | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/khepri_machine.erl b/src/khepri_machine.erl
index 5e016159..72f500c7 100644
--- a/src/khepri_machine.erl
+++ b/src/khepri_machine.erl
@@ -1545,10 +1545,18 @@ drop_expired_dedups(
   {State, Result, SideEffects},
   #{system_time := Timestamp}) ->
     Dedups = get_dedups(State),
-    Dedups1 = maps:filter(
-                fun(_CommandRef, {_Reply, Expiry}) ->
-                        Expiry >= Timestamp
-                end, Dedups),
+    %% This would look cleaner written with `maps:filter/2' but it turns out
+    %% that function is very inefficient.
+    %% TODO: explain why.
+    Dedups1 = maps:fold(
+                fun(CommandRef, {_Reply, Expiry}, Acc) ->
+                        case Expiry >= Timestamp of
+                            true ->
+                                maps:remove(CommandRef, Acc);
+                            false ->
+                                Acc
+                        end
+                end, Dedups, Dedups),
     State1 = set_dedups(State, Dedups1),
     {State1, Result, SideEffects}.