From 1550bdc78c06f5902c45c0c73eaec7d367a110ba Mon Sep 17 00:00:00 2001
From: Yedidya Feldblum <yfeldblum@meta.com>
Date: Mon, 16 Sep 2024 13:37:19 -0500
Subject: [PATCH] format std::reference_wrapper

---
 include/fmt/std.h | 11 +++++++++++
 test/std-test.cc  |  5 +++++
 2 files changed, 16 insertions(+)

diff --git a/include/fmt/std.h b/include/fmt/std.h
index 1e69b8b23fe2..403c10af1f69 100644
--- a/include/fmt/std.h
+++ b/include/fmt/std.h
@@ -17,6 +17,7 @@
 #  include <complex>
 #  include <cstdlib>
 #  include <exception>
+#  include <functional>
 #  include <memory>
 #  include <thread>
 #  include <type_traits>
@@ -699,4 +700,14 @@ template <typename T, typename Char> struct formatter<std::complex<T>, Char> {
 };
 
 FMT_END_NAMESPACE
+
+namespace std {
+
+template <typename T>
+constexpr auto format_as(std::reference_wrapper<T> ref) -> T& {
+  return ref.get();
+}
+
+} // namespace std
+
 #endif  // FMT_STD_H_
diff --git a/test/std-test.cc b/test/std-test.cc
index 424441816501..722fa73760d2 100644
--- a/test/std-test.cc
+++ b/test/std-test.cc
@@ -393,3 +393,8 @@ TEST(std_test, format_shared_ptr) {
   EXPECT_EQ(fmt::format("{}", fmt::ptr(sp.get())),
             fmt::format("{}", fmt::ptr(sp)));
 }
+
+TEST(std_test, format_reference_wrapper) {
+  int num = 35;
+  EXPECT_EQ("35", fmt::to_string(std::cref(num)));
+}