Fix clang-tidy misc-const-correctness in unit-udt_macro.cpp

The four zero-member ONLY_SERIALIZE test objects are only ever read
(via to_json), never mutated, so mark them const per clang-tidy.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/features/arbitrary_types.md

@@ -215,6 +215,24 @@ For _derived_ classes and structs, use the following macros
     nlohmann::ordered_json j = p; // keys appear in declaration order: name, address, age
     ```
 
+!!! note "Zero-member types"
+
+    All 12 `NLOHMANN_DEFINE_TYPE_*`/`NLOHMANN_DEFINE_DERIVED_TYPE_*` macros (excluding the `WITH_NAMES` variants)
+    also accept types with no member variables to serialize, producing/accepting an empty JSON object `{}`
+    (or, for the derived-type macros, just the base class's own JSON representation):
+
+    ```cpp
+    namespace ns {
+        struct marker {
+            bool operator==(const marker&) const { return true; }
+            NLOHMANN_DEFINE_TYPE_INTRUSIVE(marker)
+        };
+    }
+
+    ns::marker m{};
+    nlohmann::json j = m; // {}
+    ```
+
 !!! note "No macro for non-default-constructible types"
 
     There is currently no `NLOHMANN_DEFINE_TYPE_*`-style macro for types that are not

include/nlohmann/detail/macro_scope.hpp

@@ -587,16 +587,59 @@ void templated_json_throw(ExceptionType exception)
 
 #define NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(...) template<typename BasicJsonType, nlohmann::detail::enable_if_t<nlohmann::detail::is_basic_json<BasicJsonType>::value, int> = 0> __VA_ARGS__
 
+// Tags used to dispatch the NLOHMANN_DEFINE_TYPE_*/NLOHMANN_DEFINE_DERIVED_TYPE_*
+// macros below between a zero-member and a one-or-more-member implementation
+// (issue #4041, e.g. NLOHMANN_DEFINE_TYPE_INTRUSIVE(Type) with no further
+// arguments). NLOHMANN_JSON_TYPE_TAG(...) expands to the token 1 when
+// __VA_ARGS__ is a single token (Type alone) and to N for two or more (Type,
+// member...); NLOHMANN_JSON_DERIVED_TYPE_TAG(...) is the same idea shifted by
+// one slot for the two-token Type,BaseType prefix used by the derived-type
+// macros. Both reuse the existing 64-slot NLOHMANN_JSON_GET_MACRO dispatch
+// with one extra trailing sentinel token appended so its own trailing "..."
+// is never left completely empty at the lowest supported argument count --
+// invoking a variadic macro so that "..." matches nothing is only granted
+// unconditionally by the standard since C++20, and pre-C++20 compilers may
+// reject it under -pedantic regardless of what the macro body does.
+#define NLOHMANN_JSON_CAT_(x, y) x ## y
+#define NLOHMANN_JSON_CAT(x, y) NLOHMANN_JSON_CAT_(x, y)
+
+#define NLOHMANN_JSON_TYPE_TAG(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_GET_MACRO(__VA_ARGS__, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, 1, \
+        NLOHMANN_JSON_TYPE_TAG_SENTINEL))
+
+#define NLOHMANN_JSON_DERIVED_TYPE_TAG(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_GET_MACRO(__VA_ARGS__, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, 2, N, \
+        NLOHMANN_JSON_DERIVED_TYPE_TAG_SENTINEL))
+
 /*!
 @brief macro
 @def NLOHMANN_DEFINE_TYPE_INTRUSIVE
 @since version 3.9.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/
 */
-#define NLOHMANN_DEFINE_TYPE_INTRUSIVE(Type, ...)  \
+#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_N(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_1(Type)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType&, Type&) noexcept { })
+
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -607,10 +650,17 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/
 */
-#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(Type, ...)  \
+#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_N(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_1(Type)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType&, Type&) noexcept { })
+
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -621,9 +671,14 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.3
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/
 */
-#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(Type, ...)  \
+#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_N(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_1(Type)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); })
+
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 
@@ -633,10 +688,17 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.9.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/
 */
-#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(Type, ...)  \
+#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_N(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_1(Type)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType&, Type&) noexcept { })
+
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -647,10 +709,17 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/
 */
-#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(Type, ...)  \
+#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_N(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_1(Type)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType&, Type&) noexcept { })
+
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -661,9 +730,14 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.3
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/
 */
-#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(Type, ...)  \
+#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_N(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_1(Type)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); })
+
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 
@@ -673,10 +747,17 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(Type, BaseType, ...)  \
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_N(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_2(Type, BaseType)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
+
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -687,10 +768,17 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(Type, BaseType, ...)  \
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_N(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_2(Type, BaseType)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
+
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -701,9 +789,14 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(Type, BaseType, ...)  \
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_N(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_2(Type, BaseType)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); })
+
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 
@@ -714,10 +807,17 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(Type, BaseType, ...)  \
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_N(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_2(Type, BaseType)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
+
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -728,10 +828,17 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(Type, BaseType, ...)  \
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_N(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_2(Type, BaseType)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
+
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -742,9 +849,14 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(Type, BaseType, ...)  \
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_N(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_2(Type, BaseType)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); })
+
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 

single_include/nlohmann/json.hpp

@@ -2962,16 +2962,59 @@ void templated_json_throw(ExceptionType exception)
 
 #define NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(...) template<typename BasicJsonType, nlohmann::detail::enable_if_t<nlohmann::detail::is_basic_json<BasicJsonType>::value, int> = 0> __VA_ARGS__
 
+// Tags used to dispatch the NLOHMANN_DEFINE_TYPE_*/NLOHMANN_DEFINE_DERIVED_TYPE_*
+// macros below between a zero-member and a one-or-more-member implementation
+// (issue #4041, e.g. NLOHMANN_DEFINE_TYPE_INTRUSIVE(Type) with no further
+// arguments). NLOHMANN_JSON_TYPE_TAG(...) expands to the token 1 when
+// __VA_ARGS__ is a single token (Type alone) and to N for two or more (Type,
+// member...); NLOHMANN_JSON_DERIVED_TYPE_TAG(...) is the same idea shifted by
+// one slot for the two-token Type,BaseType prefix used by the derived-type
+// macros. Both reuse the existing 64-slot NLOHMANN_JSON_GET_MACRO dispatch
+// with one extra trailing sentinel token appended so its own trailing "..."
+// is never left completely empty at the lowest supported argument count --
+// invoking a variadic macro so that "..." matches nothing is only granted
+// unconditionally by the standard since C++20, and pre-C++20 compilers may
+// reject it under -pedantic regardless of what the macro body does.
+#define NLOHMANN_JSON_CAT_(x, y) x ## y
+#define NLOHMANN_JSON_CAT(x, y) NLOHMANN_JSON_CAT_(x, y)
+
+#define NLOHMANN_JSON_TYPE_TAG(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_GET_MACRO(__VA_ARGS__, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, 1, \
+        NLOHMANN_JSON_TYPE_TAG_SENTINEL))
+
+#define NLOHMANN_JSON_DERIVED_TYPE_TAG(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_GET_MACRO(__VA_ARGS__, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, N, N, N, N, N, N, N, N, \
+        N, N, 2, N, \
+        NLOHMANN_JSON_DERIVED_TYPE_TAG_SENTINEL))
+
 /*!
 @brief macro
 @def NLOHMANN_DEFINE_TYPE_INTRUSIVE
 @since version 3.9.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/
 */
-#define NLOHMANN_DEFINE_TYPE_INTRUSIVE(Type, ...)  \
+#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_N(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_1(Type)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType&, Type&) noexcept { })
+
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -2982,10 +3025,17 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/
 */
-#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(Type, ...)  \
+#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_N(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_1(Type)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType&, Type&) noexcept { })
+
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -2996,9 +3046,14 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.3
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_intrusive/
 */
-#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(Type, ...)  \
+#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_N(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_1(Type)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); })
+
+#define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 
@@ -3008,10 +3063,17 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.9.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/
 */
-#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(Type, ...)  \
+#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_N(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_1(Type)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType&, Type&) noexcept { })
+
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -3022,10 +3084,17 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/
 */
-#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(Type, ...)  \
+#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_N(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_1(Type)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType&, Type&) noexcept { })
+
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -3036,9 +3105,14 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.11.3
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_type_non_intrusive/
 */
-#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(Type, ...)  \
+#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_N(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_1(Type)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); })
+
+#define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 
@@ -3048,10 +3122,17 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(Type, BaseType, ...)  \
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_N(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_2(Type, BaseType)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
+
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -3062,10 +3143,17 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(Type, BaseType, ...)  \
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_N(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_2(Type, BaseType)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
+
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -3076,9 +3164,14 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(Type, BaseType, ...)  \
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_N(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_2(Type, BaseType)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); })
+
+#define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 
@@ -3089,10 +3182,17 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(Type, BaseType, ...)  \
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_N(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_2(Type, BaseType)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
+
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
@@ -3103,10 +3203,17 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(Type, BaseType, ...)  \
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_N(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_2(Type, BaseType)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); }) \
+    /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
+
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
@@ -3117,9 +3224,14 @@ void templated_json_throw(ExceptionType exception)
 @since version 3.12.0
 @sa https://json.nlohmann.me/api/macros/nlohmann_define_derived_type/
 */
-#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(Type, BaseType, ...)  \
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_N(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) })
 
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_2(Type, BaseType)  \
+    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); })
+
+#define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_CAT(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_, NLOHMANN_JSON_DERIVED_TYPE_TAG(__VA_ARGS__))(__VA_ARGS__))
+
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) })
 

tests/src/unit-udt_macro.cpp

@@ -778,6 +778,124 @@ class derived_person_only_serialize_private_3 : person_without_default_construct
     NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES(derived_person_only_serialize_private_3, person_without_default_constructor_3, "json_hair_color", hair_color)
 };
 
+// Zero-member types for issue #4041: NLOHMANN_DEFINE_TYPE_* and
+// NLOHMANN_DEFINE_DERIVED_TYPE_* must compile and produce a valid (empty)
+// JSON object when no member arguments are given.
+class empty_intrusive
+{
+  public:
+    bool operator==(const empty_intrusive& /*rhs*/) const
+    {
+        return true;
+    }
+    NLOHMANN_DEFINE_TYPE_INTRUSIVE(empty_intrusive)
+};
+
+class empty_intrusive_with_default
+{
+  public:
+    bool operator==(const empty_intrusive_with_default& /*rhs*/) const
+    {
+        return true;
+    }
+    NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT(empty_intrusive_with_default)
+};
+
+class empty_intrusive_only_serialize
+{
+  public:
+    NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE(empty_intrusive_only_serialize)
+};
+
+class empty_non_intrusive
+{
+  public:
+    bool operator==(const empty_non_intrusive& /*rhs*/) const
+    {
+        return true;
+    }
+};
+// NOLINTNEXTLINE(misc-use-internal-linkage)
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(empty_non_intrusive)
+
+class empty_non_intrusive_with_default
+{
+  public:
+    bool operator==(const empty_non_intrusive_with_default& /*rhs*/) const
+    {
+        return true;
+    }
+};
+// NOLINTNEXTLINE(misc-use-internal-linkage)
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(empty_non_intrusive_with_default)
+
+class empty_non_intrusive_only_serialize {};
+// NOLINTNEXTLINE(misc-use-internal-linkage)
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(empty_non_intrusive_only_serialize)
+
+class empty_derived_intrusive : public person_with_private_data
+{
+  public:
+    empty_derived_intrusive() = default;
+    empty_derived_intrusive(std::string name_, int age_, json metadata_)
+        : person_with_private_data(std::move(name_), age_, std::move(metadata_))
+    {}
+    NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(empty_derived_intrusive, person_with_private_data)
+};
+
+class empty_derived_intrusive_with_default : public person_with_private_data
+{
+  public:
+    empty_derived_intrusive_with_default() = default;
+    empty_derived_intrusive_with_default(std::string name_, int age_, json metadata_)
+        : person_with_private_data(std::move(name_), age_, std::move(metadata_))
+    {}
+    NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(empty_derived_intrusive_with_default, person_with_private_data)
+};
+
+class empty_derived_intrusive_only_serialize : public person_with_private_data
+{
+  public:
+    empty_derived_intrusive_only_serialize() = default;
+    empty_derived_intrusive_only_serialize(std::string name_, int age_, json metadata_)
+        : person_with_private_data(std::move(name_), age_, std::move(metadata_))
+    {}
+    NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE(empty_derived_intrusive_only_serialize, person_with_private_data)
+};
+
+class empty_derived_non_intrusive : public person_with_private_data
+{
+  public:
+    empty_derived_non_intrusive() = default;
+    empty_derived_non_intrusive(std::string name_, int age_, json metadata_)
+        : person_with_private_data(std::move(name_), age_, std::move(metadata_))
+    {}
+};
+// NOLINTNEXTLINE(misc-use-internal-linkage)
+NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(empty_derived_non_intrusive, person_with_private_data)
+
+class empty_derived_non_intrusive_with_default : public person_with_private_data
+{
+  public:
+    empty_derived_non_intrusive_with_default() = default;
+    empty_derived_non_intrusive_with_default(std::string name_, int age_, json metadata_)
+        : person_with_private_data(std::move(name_), age_, std::move(metadata_))
+    {}
+};
+// NOLINTNEXTLINE(misc-use-internal-linkage)
+NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT(empty_derived_non_intrusive_with_default, person_with_private_data)
+
+class empty_derived_non_intrusive_only_serialize : public person_with_private_data
+{
+  public:
+    empty_derived_non_intrusive_only_serialize() = default;
+    empty_derived_non_intrusive_only_serialize(std::string name_, int age_, json metadata_)
+        : person_with_private_data(std::move(name_), age_, std::move(metadata_))
+    {}
+};
+// NOLINTNEXTLINE(misc-use-internal-linkage)
+NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE(empty_derived_non_intrusive_only_serialize, person_with_private_data)
+
 } // namespace persons
 
 TEST_CASE_TEMPLATE("Serialization/deserialization via NLOHMANN_DEFINE_TYPE_INTRUSIVE and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE", Pair, // NOLINT(readability-math-missing-parentheses, bugprone-throwing-static-initialization)
@@ -1191,3 +1309,108 @@ TEST_CASE_TEMPLATE("Serialization of non-default-constructible classes via NLOHM
         }
     }
 }
+
+// Regression tests for issue #4041: NLOHMANN_DEFINE_TYPE_* and
+// NLOHMANN_DEFINE_DERIVED_TYPE_* macros must compile and produce valid
+// (empty, or base-only for the derived case) JSON objects when no member
+// arguments are given, on every supported C++ standard.
+TEST_CASE_TEMPLATE("Serialization/deserialization of zero-member types via NLOHMANN_DEFINE_TYPE_* (issue #4041)", Json, // NOLINT(readability-math-missing-parentheses, bugprone-throwing-static-initialization)
+                   nlohmann::json, nlohmann::ordered_json)
+{
+    constexpr bool is_ordered = std::is_same<Json, nlohmann::ordered_json>::value;
+    const char* const derived_dump = is_ordered
+                                     ? R"({"age":1,"name":"Erik","metadata":null})"
+                                     : R"({"age":1,"metadata":null,"name":"Erik"})";
+
+    SECTION("NLOHMANN_DEFINE_TYPE_INTRUSIVE with zero members")
+    {
+        persons::empty_intrusive obj{};
+        Json j = obj;
+        CHECK(j.dump() == "{}");
+        CHECK(j.template get<persons::empty_intrusive>() == obj);
+    }
+
+    SECTION("NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT with zero members")
+    {
+        persons::empty_intrusive_with_default obj{};
+        Json j = obj;
+        CHECK(j.dump() == "{}");
+        CHECK(j.template get<persons::empty_intrusive_with_default>() == obj);
+    }
+
+    SECTION("NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE with zero members")
+    {
+        const persons::empty_intrusive_only_serialize obj{};
+        Json j = obj;
+        CHECK(j.dump() == "{}");
+    }
+
+    SECTION("NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE with zero members")
+    {
+        persons::empty_non_intrusive obj{};
+        Json j = obj;
+        CHECK(j.dump() == "{}");
+        CHECK(j.template get<persons::empty_non_intrusive>() == obj);
+    }
+
+    SECTION("NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT with zero members")
+    {
+        persons::empty_non_intrusive_with_default obj{};
+        Json j = obj;
+        CHECK(j.dump() == "{}");
+        CHECK(j.template get<persons::empty_non_intrusive_with_default>() == obj);
+    }
+
+    SECTION("NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE with zero members")
+    {
+        const persons::empty_non_intrusive_only_serialize obj{};
+        Json j = obj;
+        CHECK(j.dump() == "{}");
+    }
+
+    SECTION("NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE with zero own members")
+    {
+        persons::empty_derived_intrusive obj{"Erik", 1, nullptr};
+        Json j = obj;
+        CHECK(j.dump() == derived_dump);
+        CHECK(j.template get<persons::empty_derived_intrusive>() == obj);
+    }
+
+    SECTION("NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT with zero own members")
+    {
+        persons::empty_derived_intrusive_with_default obj{"Erik", 1, nullptr};
+        Json j = obj;
+        CHECK(j.dump() == derived_dump);
+        CHECK(j.template get<persons::empty_derived_intrusive_with_default>() == obj);
+    }
+
+    SECTION("NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE with zero own members")
+    {
+        const persons::empty_derived_intrusive_only_serialize obj{"Erik", 1, nullptr};
+        Json j = obj;
+        CHECK(j.dump() == derived_dump);
+    }
+
+    SECTION("NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE with zero own members")
+    {
+        persons::empty_derived_non_intrusive obj{"Erik", 1, nullptr};
+        Json j = obj;
+        CHECK(j.dump() == derived_dump);
+        CHECK(j.template get<persons::empty_derived_non_intrusive>() == obj);
+    }
+
+    SECTION("NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT with zero own members")
+    {
+        persons::empty_derived_non_intrusive_with_default obj{"Erik", 1, nullptr};
+        Json j = obj;
+        CHECK(j.dump() == derived_dump);
+        CHECK(j.template get<persons::empty_derived_non_intrusive_with_default>() == obj);
+    }
+
+    SECTION("NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE with zero own members")
+    {
+        const persons::empty_derived_non_intrusive_only_serialize obj{"Erik", 1, nullptr};
+        Json j = obj;
+        CHECK(j.dump() == derived_dump);
+    }
+}