From 9c31d543890ce0b1b5fe5a4bb07465a289cc60ec Mon Sep 17 00:00:00 2001
From: Florian Albrechtskirchinger <falbrechtskirchinger@gmail.com>
Date: Mon, 13 Jun 2022 13:21:55 +0200
Subject: [PATCH] Add to_json() for std::vector<bool>::reference (#3534)

---
 include/nlohmann/detail/conversions/to_json.hpp | 7 +++++++
 single_include/nlohmann/json.hpp                | 7 +++++++
 tests/src/unit-constructor1.cpp                 | 7 +++++++
 3 files changed, 21 insertions(+)

diff --git a/include/nlohmann/detail/conversions/to_json.hpp b/include/nlohmann/detail/conversions/to_json.hpp
index fde46ef7c..b59077338 100644
--- a/include/nlohmann/detail/conversions/to_json.hpp
+++ b/include/nlohmann/detail/conversions/to_json.hpp
@@ -272,6 +272,13 @@ inline void to_json(BasicJsonType& j, T b) noexcept
     external_constructor<value_t::boolean>::construct(j, b);
 }
 
+template<typename BasicJsonType,
+         enable_if_t<std::is_convertible<const std::vector<bool>::reference&, typename BasicJsonType::boolean_t>::value, int> = 0>
+inline void to_json(BasicJsonType& j, const std::vector<bool>::reference& b) noexcept
+{
+    external_constructor<value_t::boolean>::construct(j, static_cast<typename BasicJsonType::boolean_t>(b));
+}
+
 template<typename BasicJsonType, typename CompatibleString,
          enable_if_t<std::is_constructible<typename BasicJsonType::string_t, CompatibleString>::value, int> = 0>
 inline void to_json(BasicJsonType& j, const CompatibleString& s)
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index c5fd3fd0b..4a73ce5d3 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -5253,6 +5253,13 @@ inline void to_json(BasicJsonType& j, T b) noexcept
     external_constructor<value_t::boolean>::construct(j, b);
 }
 
+template<typename BasicJsonType,
+         enable_if_t<std::is_convertible<const std::vector<bool>::reference&, typename BasicJsonType::boolean_t>::value, int> = 0>
+inline void to_json(BasicJsonType& j, const std::vector<bool>::reference& b) noexcept
+{
+    external_constructor<value_t::boolean>::construct(j, static_cast<typename BasicJsonType::boolean_t>(b));
+}
+
 template<typename BasicJsonType, typename CompatibleString,
          enable_if_t<std::is_constructible<typename BasicJsonType::string_t, CompatibleString>::value, int> = 0>
 inline void to_json(BasicJsonType& j, const CompatibleString& s)
diff --git a/tests/src/unit-constructor1.cpp b/tests/src/unit-constructor1.cpp
index 195521226..21f21e380 100644
--- a/tests/src/unit-constructor1.cpp
+++ b/tests/src/unit-constructor1.cpp
@@ -474,6 +474,13 @@ TEST_CASE("constructors")
             json j(false);
             CHECK(j.type() == json::value_t::boolean);
         }
+
+        SECTION("from std::vector<bool>::refrence")
+        {
+            std::vector<bool> v{true};
+            json j(v[0]);
+            CHECK(j.type() == json::value_t::boolean);
+        }
     }
 
     SECTION("create a binary (explicit)")