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diff --git a/src/boost/libs/hana/test/fold_left/ref.cpp b/src/boost/libs/hana/test/fold_left/ref.cpp
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+++ b/src/boost/libs/hana/test/fold_left/ref.cpp
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+// Copyright Louis Dionne 2013-2017
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+
+#include <boost/hana/assert.hpp>
+#include <boost/hana/at.hpp>
+#include <boost/hana/fold_left.hpp>
+#include <boost/hana/tuple.hpp>
+namespace hana = boost::hana;
+
+//
+// Make sure that we can fold_left and take arguments by reference.
+//
+
+int main() {
+    // with state
+    {
+        auto xs = hana::make_tuple(1, 2, 3);
+        int state = 99;
+
+        int& three = hana::fold_left(xs, state, [](int&, int& i) -> int& {
+            return i;
+        });
+        BOOST_HANA_RUNTIME_CHECK(three == 3);
+        three = 10;
+        BOOST_HANA_RUNTIME_CHECK(hana::at_c<2>(xs) == 10);
+    }
+
+    // without state
+    {
+        auto xs = hana::make_tuple(1, 2, 3);
+
+        int& three = hana::fold_left(xs, [](int&, int& i) -> int& {
+            return i;
+        });
+        BOOST_HANA_RUNTIME_CHECK(three == 3);
+        three = 10;
+        BOOST_HANA_RUNTIME_CHECK(hana::at_c<2>(xs) == 10);
+    }
+}