From 43c4b61bdd3669c2cc08d50f10401f0b04befcc9 Mon Sep 17 00:00:00 2001
From: Neil <nyamatongwe@gmail.com>
Date: Thu, 18 Mar 2021 19:04:08 +1100
Subject: std::optional is a basic vocabulary type that may be used widely so
 include almost everywhere.

---
 src/ContractionState.cxx | 1 +
 1 file changed, 1 insertion(+)

(limited to 'src/ContractionState.cxx')

diff --git a/src/ContractionState.cxx b/src/ContractionState.cxx
index af1c88bb7..551879c0c 100644
--- a/src/ContractionState.cxx
+++ b/src/ContractionState.cxx
@@ -12,6 +12,7 @@
 #include <stdexcept>
 #include <string_view>
 #include <vector>
+#include <optional>
 #include <algorithm>
 #include <memory>
 
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