Added support for `nullptr` (closes #998)

CHANGELOG.md

@@ -11,6 +11,7 @@ HEAD
 * Added `ARDUINOJSON_ENABLE_INFINITY` (default=0) to enable Infinity in JSON
 * Removed implicit conversion in comparison operators (issue #998)
 * Added lexicographical comparison for `JsonVariant`
+* Added support for `nullptr` (issue #998)
 
 > ### BREAKING CHANGES
 > 

src/ArduinoJson/Configuration.hpp

@@ -12,8 +12,10 @@
 
 #if __cplusplus >= 201103L
 #define ARDUINOJSON_HAS_LONG_LONG 1
+#define ARDUINOJSON_HAS_NULLPTR 1
 #else
 #define ARDUINOJSON_HAS_LONG_LONG 0
+#define ARDUINOJSON_HAS_NULLPTR 0
 #endif
 
 // Small or big machine?

src/ArduinoJson/Operators/VariantComparisons.hpp

@@ -88,6 +88,27 @@ struct Comparer<bool, void> {
   void visitNull() {}
 };
 
+#if ARDUINOJSON_HAS_NULLPTR
+template <>
+struct Comparer<decltype(nullptr), void> {
+  int result;
+
+  explicit Comparer(decltype(nullptr)) : result(1) {}
+
+  void visitArray(const CollectionData &) {}
+  void visitObject(const CollectionData &) {}
+  void visitFloat(Float) {}
+  void visitString(const char *) {}
+  void visitRawJson(const char *, size_t) {}
+  void visitNegativeInteger(UInt) {}
+  void visitPositiveInteger(UInt) {}
+  void visitBoolean(bool) {}
+  void visitNull() {
+    result = 0;
+  }
+};
+#endif
+
 template <typename TVariant>
 class VariantComparisons {
  private:

test/MixedConfiguration/CMakeLists.txt

@@ -6,12 +6,13 @@
 set(CMAKE_CXX_STANDARD 11)
 
 add_executable(MixedConfigurationTests
+	cpp11.cpp
 	decode_unicode_0.cpp
 	decode_unicode_1.cpp
-	enable_nan_0.cpp
-	enable_nan_1.cpp
 	enable_infinity_0.cpp
 	enable_infinity_1.cpp
+	enable_nan_0.cpp
+	enable_nan_1.cpp
 	use_double_0.cpp
 	use_double_1.cpp
 	use_long_long_0.cpp

test/MixedConfiguration/cpp11.cpp

@@ -0,0 +1,31 @@
+#include <ArduinoJson.h>
+
+#include <catch.hpp>
+
+#if __cplusplus >= 201103L
+
+TEST_CASE("nullptr") {
+  DynamicJsonDocument doc(4096);
+  JsonVariant variant = doc.to<JsonVariant>();
+
+  SECTION("JsonVariant == nullptr") {
+    REQUIRE((variant == nullptr));
+    REQUIRE_FALSE((variant != nullptr));
+  }
+
+  SECTION("JsonVariant != nullptr") {
+    variant.set(42);
+
+    REQUIRE_FALSE((variant == nullptr));
+    REQUIRE((variant != nullptr));
+  }
+
+  SECTION("JsonVariant.set(nullptr)") {
+    variant.set(42);
+    variant.set(nullptr);
+
+    REQUIRE(variant.isNull());
+  }
+}
+
+#endif