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] :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 c389dca7a..34a9c327e 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 a1def699f..040ba795f 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 e2a68e6f5..8cfebd025 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 8477cf639..c0c52f605 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