From 5a866fe852c698163d0e95f0f48a64528eca45f6 Mon Sep 17 00:00:00 2001
From: Zhanwei Wang <wang@hashdata.cn>
Date: Mon, 14 Aug 2023 23:34:31 +0800
Subject: [PATCH] Add formatter for std::atomic (#3574)

---
 include/fmt/std.h | 14 +++++++++++++-
 test/std-test.cc  |  8 ++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/fmt/std.h b/include/fmt/std.h
index b0e78e10..5cfe1d87 100644
--- a/include/fmt/std.h
+++ b/include/fmt/std.h
@@ -8,6 +8,7 @@
 #ifndef FMT_STD_H_
 #define FMT_STD_H_
 
+#include <atomic>
 #include <bitset>
 #include <cstdlib>
 #include <exception>
@@ -435,6 +436,17 @@ struct formatter<BitRef, Char,
   }
 };
 
-FMT_END_NAMESPACE
+FMT_EXPORT
+template <typename T, typename Char>
+struct formatter<std::atomic<T>, Char,
+                 enable_if_t<is_formattable<T, Char>::value>>
+    : formatter<T, Char> {
+  template <typename FormatContext>
+  auto format(const std::atomic<T>& v, FormatContext& ctx) const
+      -> decltype(ctx.out()) {
+    return formatter<T, Char>::format(v.load(), ctx);
+  }
+};
 
+FMT_END_NAMESPACE
 #endif  // FMT_STD_H_
diff --git a/test/std-test.cc b/test/std-test.cc
index 17b4792c..d0617a73 100644
--- a/test/std-test.cc
+++ b/test/std-test.cc
@@ -236,3 +236,11 @@ TEST(std_test, format_const_bit_reference) {
   const std::vector<bool> v = {true, false};
   EXPECT_EQ(fmt::format("{} {}", v[0], v[1]), "true false");
 }
+
+TEST(std_test, format_atomic) {
+  std::atomic<bool> b(false);
+  EXPECT_EQ(fmt::format("{}", b), "false");
+
+  const std::atomic<bool> cb(true);
+  EXPECT_EQ(fmt::format("{}", cb), "true");
+}