From df30a0ea07ff9b922dc3ea49047f996446cf38c6 Mon Sep 17 00:00:00 2001
From: Niels Lohmann <mail@nlohmann.me>
Date: Sat, 23 Nov 2019 00:21:33 +0100
Subject: [PATCH 1/7] :construction: conversions for std::optional

---
 .../nlohmann/detail/conversions/from_json.hpp | 19 ++++++
 .../nlohmann/detail/conversions/to_json.hpp   | 20 ++++++
 single_include/nlohmann/json.hpp              | 39 ++++++++++++
 test/src/unit-conversions.cpp                 | 62 ++++++++++++++++++-
 4 files changed, 139 insertions(+), 1 deletion(-)

diff --git a/include/nlohmann/detail/conversions/from_json.hpp b/include/nlohmann/detail/conversions/from_json.hpp
index c389dca7ad..34a9c327ed 100644
--- a/include/nlohmann/detail/conversions/from_json.hpp
+++ b/include/nlohmann/detail/conversions/from_json.hpp
@@ -13,6 +13,10 @@
 #include <utility> // pair, declval
 #include <valarray> // valarray
 
+#ifdef JSON_HAS_CPP_17
+    #include <optional> // optional
+#endif
+
 #include <nlohmann/detail/exceptions.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/meta/cpp_future.hpp>
@@ -33,6 +37,21 @@ void from_json(const BasicJsonType& j, typename std::nullptr_t& n)
     n = nullptr;
 }
 
+#ifdef JSON_HAS_CPP_17
+template<typename BasicJsonType, typename T>
+void from_json(const BasicJsonType& j, std::optional<T>& opt)
+{
+    if (j.is_null())
+    {
+        opt = std::nullopt;
+    }
+    else
+    {
+        opt = j.template get<T>();
+    }
+}
+#endif
+
 // overloads for basic_json template parameters
 template<typename BasicJsonType, typename ArithmeticType,
          enable_if_t<std::is_arithmetic<ArithmeticType>::value and
diff --git a/include/nlohmann/detail/conversions/to_json.hpp b/include/nlohmann/detail/conversions/to_json.hpp
index a1def699fd..040ba795f9 100644
--- a/include/nlohmann/detail/conversions/to_json.hpp
+++ b/include/nlohmann/detail/conversions/to_json.hpp
@@ -10,6 +10,10 @@
 #include <valarray> // valarray
 #include <vector> // vector
 
+#ifdef JSON_HAS_CPP_17
+    #include <optional> // optional
+#endif
+
 #include <nlohmann/detail/iterators/iteration_proxy.hpp>
 #include <nlohmann/detail/meta/cpp_future.hpp>
 #include <nlohmann/detail/meta/type_traits.hpp>
@@ -198,6 +202,22 @@ struct external_constructor<value_t::object>
 // to_json //
 /////////////
 
+#ifdef JSON_HAS_CPP_17
+template<typename BasicJsonType, typename T,
+         enable_if_t<std::is_constructible<BasicJsonType, T>::value, int> = 0>
+void to_json(BasicJsonType& j, const std::optional<T>& opt)
+{
+    if (opt.has_value())
+    {
+        j = *opt;
+    }
+    else
+    {
+        j = nullptr;
+    }
+}
+#endif
+
 template<typename BasicJsonType, typename T,
          enable_if_t<std::is_same<T, typename BasicJsonType::boolean_t>::value, int> = 0>
 void to_json(BasicJsonType& j, T b) noexcept
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index e2a68e6f58..8cfebd0254 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -69,6 +69,10 @@ SOFTWARE.
 #include <utility> // pair, declval
 #include <valarray> // valarray
 
+#ifdef JSON_HAS_CPP_17
+    #include <optional> // optional
+#endif
+
 // #include <nlohmann/detail/exceptions.hpp>
 
 
@@ -2904,6 +2908,21 @@ void from_json(const BasicJsonType& j, typename std::nullptr_t& n)
     n = nullptr;
 }
 
+#ifdef JSON_HAS_CPP_17
+template<typename BasicJsonType, typename T>
+void from_json(const BasicJsonType& j, std::optional<T>& opt)
+{
+    if (j.is_null())
+    {
+        opt = std::nullopt;
+    }
+    else
+    {
+        opt = j.template get<T>();
+    }
+}
+#endif
+
 // overloads for basic_json template parameters
 template<typename BasicJsonType, typename ArithmeticType,
          enable_if_t<std::is_arithmetic<ArithmeticType>::value and
@@ -3272,6 +3291,10 @@ constexpr const auto& from_json = detail::static_const<detail::from_json_fn>::va
 #include <valarray> // valarray
 #include <vector> // vector
 
+#ifdef JSON_HAS_CPP_17
+    #include <optional> // optional
+#endif
+
 // #include <nlohmann/detail/iterators/iteration_proxy.hpp>
 
 
@@ -3642,6 +3665,22 @@ struct external_constructor<value_t::object>
 // to_json //
 /////////////
 
+#ifdef JSON_HAS_CPP_17
+template<typename BasicJsonType, typename T,
+         enable_if_t<std::is_constructible<BasicJsonType, T>::value, int> = 0>
+void to_json(BasicJsonType& j, const std::optional<T>& opt)
+{
+    if (opt.has_value())
+    {
+        j = *opt;
+    }
+    else
+    {
+        j = nullptr;
+    }
+}
+#endif
+
 template<typename BasicJsonType, typename T,
          enable_if_t<std::is_same<T, typename BasicJsonType::boolean_t>::value, int> = 0>
 void to_json(BasicJsonType& j, T b) noexcept
diff --git a/test/src/unit-conversions.cpp b/test/src/unit-conversions.cpp
index 8477cf6392..c0c52f605b 100644
--- a/test/src/unit-conversions.cpp
+++ b/test/src/unit-conversions.cpp
@@ -50,6 +50,7 @@ using nlohmann::json;
 #endif
 
 #if defined(JSON_HAS_CPP_17)
+    #include <optional>
     #include <string_view>
 #endif
 
@@ -189,7 +190,6 @@ TEST_CASE("value conversion")
         }
     }
 
-
     SECTION("get an object (implicit)")
     {
         json::object_t o_reference = {{"object", json::object()},
@@ -1575,3 +1575,63 @@ TEST_CASE("JSON to enum mapping")
         CHECK(TS_INVALID == json("what?").get<TaskState>());
     }
 }
+
+#ifdef JSON_HAS_CPP_17
+TEST_CASE("std::optional")
+{
+    SECTION("null")
+    {
+        json j_null;
+        std::optional<std::string> opt_null;
+
+        CHECK(json(opt_null) == j_null);
+        //CHECK(std::optional<std::string>(j_null) == std::nullopt);
+    }
+
+    SECTION("string")
+    {
+        json j_string = "string";
+        std::optional<std::string> opt_string = "string";
+
+        CHECK(json(opt_string) == j_string);
+        CHECK(std::optional<std::string>(j_string) == opt_string);
+    }
+
+    SECTION("bool")
+    {
+        json j_bool = true;
+        std::optional<bool> opt_bool = true;
+
+        CHECK(json(opt_bool) == j_bool);
+        CHECK(std::optional<bool>(j_bool) == opt_bool);
+    }
+
+    SECTION("number")
+    {
+        json j_number = 1;
+        std::optional<int> opt_int = 1;
+
+        CHECK(json(opt_int) == j_number);
+        CHECK(std::optional<int>(j_number) == opt_int);
+    }
+
+    SECTION("array")
+    {
+        json j_array = {1, 2, 3};
+        std::optional<std::vector<int>> opt_array = {{1, 2, 3}};
+
+        CHECK(json(opt_array) == j_array);
+        CHECK(std::optional<std::vector<int>>(j_array) == opt_array);
+    }
+
+    SECTION("object")
+    {
+        json j_object = {{"one", 1}, {"two", 2}};
+        std::map<std::string, int> m {{"one", 1}, {"two", 2}};
+        std::optional<std::map<std::string, int>> opt_object = m;
+
+        CHECK(json(opt_object) == j_object);
+        CHECK(std::optional<std::map<std::string, int>>(j_object) == opt_object);
+    }
+}
+#endif

From 1359c56137363fa3ca9eb91fa8ba648ab22fa84f Mon Sep 17 00:00:00 2001
From: Niels Lohmann <mail@nlohmann.me>
Date: Sat, 23 Nov 2019 13:29:47 +0100
Subject: [PATCH 2/7] :checkered_flag: fix <optional> inclusion

---
 include/nlohmann/detail/conversions/from_json.hpp |  6 +++++-
 include/nlohmann/detail/conversions/to_json.hpp   |  6 +++++-
 single_include/nlohmann/json.hpp                  | 12 ++++++++++--
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/include/nlohmann/detail/conversions/from_json.hpp b/include/nlohmann/detail/conversions/from_json.hpp
index 34a9c327ed..ca16c71122 100644
--- a/include/nlohmann/detail/conversions/from_json.hpp
+++ b/include/nlohmann/detail/conversions/from_json.hpp
@@ -14,7 +14,11 @@
 #include <valarray> // valarray
 
 #ifdef JSON_HAS_CPP_17
-    #include <optional> // optional
+    #if __has_include(<optional>)
+        #include <optional>
+    #elif __has_include(<experimental/optional>)
+        #include <experimental/optional>
+    #endif
 #endif
 
 #include <nlohmann/detail/exceptions.hpp>
diff --git a/include/nlohmann/detail/conversions/to_json.hpp b/include/nlohmann/detail/conversions/to_json.hpp
index 040ba795f9..e9a0f6471c 100644
--- a/include/nlohmann/detail/conversions/to_json.hpp
+++ b/include/nlohmann/detail/conversions/to_json.hpp
@@ -11,7 +11,11 @@
 #include <vector> // vector
 
 #ifdef JSON_HAS_CPP_17
-    #include <optional> // optional
+    #if __has_include(<optional>)
+        #include <optional>
+    #elif __has_include(<experimental/optional>)
+        #include <experimental/optional>
+    #endif
 #endif
 
 #include <nlohmann/detail/iterators/iteration_proxy.hpp>
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 8cfebd0254..ba2575b621 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -70,7 +70,11 @@ SOFTWARE.
 #include <valarray> // valarray
 
 #ifdef JSON_HAS_CPP_17
-    #include <optional> // optional
+    #if __has_include(<optional>)
+        #include <optional>
+    #elif __has_include(<experimental/optional>)
+        #include <experimental/optional>
+    #endif
 #endif
 
 // #include <nlohmann/detail/exceptions.hpp>
@@ -3292,7 +3296,11 @@ constexpr const auto& from_json = detail::static_const<detail::from_json_fn>::va
 #include <vector> // vector
 
 #ifdef JSON_HAS_CPP_17
-    #include <optional> // optional
+    #if __has_include(<optional>)
+        #include <optional>
+    #elif __has_include(<experimental/optional>)
+        #include <experimental/optional>
+    #endif
 #endif
 
 // #include <nlohmann/detail/iterators/iteration_proxy.hpp>

From 713038fa278243dfdb244d1faffce60b16fccf50 Mon Sep 17 00:00:00 2001
From: Niels Lohmann <mail@nlohmann.me>
Date: Sat, 23 Nov 2019 14:40:15 +0100
Subject: [PATCH 3/7] :green_heart: overwork tests

---
 test/src/unit-conversions.cpp | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/test/src/unit-conversions.cpp b/test/src/unit-conversions.cpp
index c0c52f605b..0cdecdd79e 100644
--- a/test/src/unit-conversions.cpp
+++ b/test/src/unit-conversions.cpp
@@ -1617,21 +1617,20 @@ TEST_CASE("std::optional")
 
     SECTION("array")
     {
-        json j_array = {1, 2, 3};
-        std::optional<std::vector<int>> opt_array = {{1, 2, 3}};
+        json j_array = {1, 2, nullptr};
+        std::vector<std::optional<int>> opt_array = {{1, 2, std::nullopt}};
 
         CHECK(json(opt_array) == j_array);
-        CHECK(std::optional<std::vector<int>>(j_array) == opt_array);
+        CHECK(std::vector<std::optional<int>>(j_array) == opt_array);
     }
 
     SECTION("object")
     {
-        json j_object = {{"one", 1}, {"two", 2}};
-        std::map<std::string, int> m {{"one", 1}, {"two", 2}};
-        std::optional<std::map<std::string, int>> opt_object = m;
+        json j_object = {{"one", 1}, {"two", 2}, {"zero", nullptr}};
+        std::map<std::string, std::optional<int>> opt_object {{"one", 1}, {"two", 2}, {"zero", std::nullopt}};
 
         CHECK(json(opt_object) == j_object);
-        CHECK(std::optional<std::map<std::string, int>>(j_object) == opt_object);
+        CHECK(std::map<std::string, std::optional<int>>(j_object) == opt_object);
     }
 }
 #endif

From 1b846c9d8191a50c30d63f88a4ae597419ae5735 Mon Sep 17 00:00:00 2001
From: Markus Palonen <markus.palonen@gmail.com>
Date: Tue, 17 Dec 2019 16:25:35 +0200
Subject: [PATCH 4/7] Use JSON_HAS_CPP_17 only after it has been defined

---
 .../nlohmann/detail/conversions/from_json.hpp |  8 -------
 .../nlohmann/detail/conversions/to_json.hpp   |  8 -------
 include/nlohmann/detail/macro_scope.hpp       |  8 +++++++
 single_include/nlohmann/json.hpp              | 24 +++++++------------
 4 files changed, 16 insertions(+), 32 deletions(-)

diff --git a/include/nlohmann/detail/conversions/from_json.hpp b/include/nlohmann/detail/conversions/from_json.hpp
index ca16c71122..28b10486ae 100644
--- a/include/nlohmann/detail/conversions/from_json.hpp
+++ b/include/nlohmann/detail/conversions/from_json.hpp
@@ -13,14 +13,6 @@
 #include <utility> // pair, declval
 #include <valarray> // valarray
 
-#ifdef JSON_HAS_CPP_17
-    #if __has_include(<optional>)
-        #include <optional>
-    #elif __has_include(<experimental/optional>)
-        #include <experimental/optional>
-    #endif
-#endif
-
 #include <nlohmann/detail/exceptions.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/meta/cpp_future.hpp>
diff --git a/include/nlohmann/detail/conversions/to_json.hpp b/include/nlohmann/detail/conversions/to_json.hpp
index e9a0f6471c..4666833635 100644
--- a/include/nlohmann/detail/conversions/to_json.hpp
+++ b/include/nlohmann/detail/conversions/to_json.hpp
@@ -10,14 +10,6 @@
 #include <valarray> // valarray
 #include <vector> // vector
 
-#ifdef JSON_HAS_CPP_17
-    #if __has_include(<optional>)
-        #include <optional>
-    #elif __has_include(<experimental/optional>)
-        #include <experimental/optional>
-    #endif
-#endif
-
 #include <nlohmann/detail/iterators/iteration_proxy.hpp>
 #include <nlohmann/detail/meta/cpp_future.hpp>
 #include <nlohmann/detail/meta/type_traits.hpp>
diff --git a/include/nlohmann/detail/macro_scope.hpp b/include/nlohmann/detail/macro_scope.hpp
index 27dddc6be7..16200502bf 100644
--- a/include/nlohmann/detail/macro_scope.hpp
+++ b/include/nlohmann/detail/macro_scope.hpp
@@ -27,6 +27,14 @@
     #define JSON_HAS_CPP_14
 #endif
 
+#ifdef JSON_HAS_CPP_17
+    #if __has_include(<optional>)
+        #include <optional>
+    #elif __has_include(<experimental/optional>)
+        #include <experimental/optional>
+    #endif
+#endif
+
 // disable float-equal warnings on GCC/clang
 #if defined(__clang__) || defined(__GNUC__) || defined(__GNUG__)
     #pragma GCC diagnostic push
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index ba2575b621..4cd8ed9fcb 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -69,14 +69,6 @@ SOFTWARE.
 #include <utility> // pair, declval
 #include <valarray> // valarray
 
-#ifdef JSON_HAS_CPP_17
-    #if __has_include(<optional>)
-        #include <optional>
-    #elif __has_include(<experimental/optional>)
-        #include <experimental/optional>
-    #endif
-#endif
-
 // #include <nlohmann/detail/exceptions.hpp>
 
 
@@ -1739,6 +1731,14 @@ JSON_HEDLEY_DIAGNOSTIC_POP
     #define JSON_HAS_CPP_14
 #endif
 
+#ifdef JSON_HAS_CPP_17
+    #if __has_include(<optional>)
+        #include <optional>
+    #elif __has_include(<experimental/optional>)
+        #include <experimental/optional>
+    #endif
+#endif
+
 // disable float-equal warnings on GCC/clang
 #if defined(__clang__) || defined(__GNUC__) || defined(__GNUG__)
     #pragma GCC diagnostic push
@@ -3295,14 +3295,6 @@ constexpr const auto& from_json = detail::static_const<detail::from_json_fn>::va
 #include <valarray> // valarray
 #include <vector> // vector
 
-#ifdef JSON_HAS_CPP_17
-    #if __has_include(<optional>)
-        #include <optional>
-    #elif __has_include(<experimental/optional>)
-        #include <experimental/optional>
-    #endif
-#endif
-
 // #include <nlohmann/detail/iterators/iteration_proxy.hpp>
 
 

From 6b31375c7c489f4a9ba9910c0eda281e20e9fbce Mon Sep 17 00:00:00 2001
From: Niels Lohmann <mail@nlohmann.me>
Date: Thu, 19 Dec 2019 12:25:27 +0100
Subject: [PATCH 5/7] :alembic: set CXXFLAGS

---
 .travis.yml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/.travis.yml b/.travis.yml
index 76e1e5aba6..987538aaa0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -329,6 +329,7 @@ script:
 
   # make sure CXX is correctly set
   - if [[ "${COMPILER}" != "" ]]; then export CXX=${COMPILER}; fi
+  - if [[ "${CXXFLAGS}" != "" ]]; then export CXXFLAGS=${CXXFLAGS}; fi
   # by default, use the single-header version
   - if [[ "${MULTIPLE_HEADERS}" == "" ]]; then export MULTIPLE_HEADERS=OFF; fi
 

From 007c6c4bc537042d117298edc8c4008d1da1dec0 Mon Sep 17 00:00:00 2001
From: Niels Lohmann <mail@nlohmann.me>
Date: Sat, 16 May 2020 19:37:18 +0200
Subject: [PATCH 6/7] :white_check_mark: update tests

---
 test/src/unit-conversions.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/src/unit-conversions.cpp b/test/src/unit-conversions.cpp
index 0cdecdd79e..1850126214 100644
--- a/test/src/unit-conversions.cpp
+++ b/test/src/unit-conversions.cpp
@@ -1585,7 +1585,7 @@ TEST_CASE("std::optional")
         std::optional<std::string> opt_null;
 
         CHECK(json(opt_null) == j_null);
-        //CHECK(std::optional<std::string>(j_null) == std::nullopt);
+        CHECK(std::optional<std::string>(j_null) == std::nullopt);
     }
 
     SECTION("string")

From f25bf312fc4ee49f1bc38ef1ccd27b499261fc57 Mon Sep 17 00:00:00 2001
From: Niels Lohmann <mail@nlohmann.me>
Date: Sun, 17 May 2020 13:58:09 +0200
Subject: [PATCH 7/7] :checkered_flag: include right <optional> header

---
 test/src/unit-conversions.cpp | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/test/src/unit-conversions.cpp b/test/src/unit-conversions.cpp
index 1850126214..624b3898d4 100644
--- a/test/src/unit-conversions.cpp
+++ b/test/src/unit-conversions.cpp
@@ -49,8 +49,15 @@ using nlohmann::json;
     #define JSON_HAS_CPP_14
 #endif
 
+#ifdef JSON_HAS_CPP_17
+    #if __has_include(<optional>)
+        #include <optional>
+    #elif __has_include(<experimental/optional>)
+        #include <experimental/optional>
+    #endif
+#endif
+
 #if defined(JSON_HAS_CPP_17)
-    #include <optional>
     #include <string_view>
 #endif