Document zero-member support in the macro API reference

docs/mkdocs/docs/features/arbitrary_types.md already gained a note, but the three api/macros pages are where the parameter contract is actually specified and they still described member as a non-empty list. State that the list may be empty on each page, and add a note showing what the zero-member case generates: an empty JSON object for the plain macros, and base-type-only serialization for the derived ones. Both notes record that the WITH_NAMES variants do not support this. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Name the zero-member macro bodies by intent, not argument count
2026-08-21 16:43:17 +00:00 · 2026-08-20 09:01:11 +02:00 · 2026-08-19 23:05:45 +02:00 · 2026-08-19 21:03:08 +02:00 · 2026-07-12 06:37:49 +00:00 · 2026-07-11 23:55:43 +02:00
7 changed files with 582 additions and 27 deletions
@@ -57,7 +57,8 @@ Summary:
 :   name of the base type (class, struct) `type` is derived from

 `member` (in)
-:   name of the member variable to serialize/deserialize; up to 63 members can be given as a comma-separated list
+:   name of the member variable to serialize/deserialize; up to 63 members can be given as a comma-separated
+    list, which may also be empty

 ## Default definition

@@ -127,6 +128,20 @@ void to_json(BasicJsonType& j, const B& b) {
    - Macros 4, 5, and 6 have the same prerequisites of [NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE](nlohmann_define_type_non_intrusive.md).
    - Serialization/deserialization of base types must be defined.

+!!! info "Derived types without own members"
+
+    The member list may be empty. The macro then generates a `to_json`/`from_json` pair that only delegates to
+    the base type, so `type` serializes exactly like `base_type`:
+
+    ```cpp
+    struct derived : base
+    {
+        NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(derived, base)
+    };
+    ```
+
+    The `WITH_NAMES` variants do not support this.
+
 !!! warning "Implementation limits"

    See Implementation limits for [NLOHMANN_DEFINE_TYPE_INTRUSIVE](nlohmann_define_type_intrusive.md) and
@@ -33,7 +33,8 @@ Summary:
 :   name of the type (class, struct) to serialize/deserialize

 `member` (in)
-:   name of the member variable to serialize/deserialize; up to 63 members can be given as a comma-separated list
+:   name of the member variable to serialize/deserialize; up to 63 members can be given as a comma-separated
+    list, which may also be empty

 ## Default definition

@@ -58,6 +59,20 @@ See the examples below for the concrete generated code.

 [GetNonDefNonCopy]: ../../features/arbitrary_types.md#how-can-i-use-get-for-non-default-constructiblenon-copyable-types

+!!! info "Types without members"
+
+    The member list may be empty. The macro then generates a `to_json` that produces an empty JSON object
+    `#!json {}`, and a `from_json` that reads no members:
+
+    ```cpp
+    struct marker
+    {
+        NLOHMANN_DEFINE_TYPE_INTRUSIVE(marker)
+    };
+    ```
+
+    The `WITH_NAMES` variants do not support this.
+
 !!! warning "Implementation limits"

    - The current implementation is limited to at most 63 member variables. If you want to serialize/deserialize types
@@ -33,7 +33,8 @@ Summary:
 :   name of the type (class, struct) to serialize/deserialize

 `member` (in)
-:   name of the (public) member variable to serialize/deserialize; up to 63 members can be given as a comma-separated list
+:   name of the (public) member variable to serialize/deserialize; up to 63 members can be given as a
+    comma-separated list, which may also be empty

 ## Default definition

@@ -59,6 +60,18 @@ See the examples below for the concrete generated code.

 [GetNonDefNonCopy]: ../../features/arbitrary_types.md#how-can-i-use-get-for-non-default-constructiblenon-copyable-types

+!!! info "Types without members"
+
+    The member list may be empty. The macro then generates a `to_json` that produces an empty JSON object
+    `#!json {}`, and a `from_json` that reads no members:
+
+    ```cpp
+    struct marker {};
+    NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(marker)
+    ```
+
+    The `WITH_NAMES` variants do not support this.
+
 !!! warning "Implementation limits"

    - The current implementation is limited to at most 63 member variables. If you want to serialize/deserialize types
@@ -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
@@ -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 EMPTY when
+// __VA_ARGS__ is a single token (Type alone) and to MEMBERS for two or more
+// (Type, member...), naming the body the public macro dispatches to. It
+// reuses 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.
+//
+// NLOHMANN_JSON_DERIVED_TYPE_TAG(...) answers the same question for the
+// derived-type macros, whose fixed prefix is Type,BaseType. It drops the
+// leading Type and defers to NLOHMANN_JSON_TYPE_TAG rather than shifting the
+// slot table by one: NLOHMANN_JSON_GET_MACRO only resolves 64 positional
+// arguments, so tagging Type,BaseType,member... directly would run out one
+// slot early and cap the derived-type macros at 62 members instead of the 63
+// that NLOHMANN_JSON_PASTE supports.
+#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__, \
+        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
+        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
+        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
+        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
+        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
+        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
+        MEMBERS, MEMBERS, MEMBERS, EMPTY, \
+        NLOHMANN_JSON_TYPE_TAG_SENTINEL))
+
+#define NLOHMANN_JSON_DERIVED_TYPE_TAG_(Type, ...) NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__)
+#define NLOHMANN_JSON_DERIVED_TYPE_TAG(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DERIVED_TYPE_TAG_(__VA_ARGS__))
+
 /*!
@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_MEMBERS(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_EMPTY(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 +650,15 @@ 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_MEMBERS(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__)) })

+// identical to NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY: with no members there is nothing to default
+#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_EMPTY(Type) NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY(Type)
+
+#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 +669,14 @@ 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_MEMBERS(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_EMPTY(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 +686,17 @@ 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_MEMBERS(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_EMPTY(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 +707,15 @@ 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_MEMBERS(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__)) })

+// identical to NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY: with no members there is nothing to default
+#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_EMPTY(Type) NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY(Type)
+
+#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 +726,14 @@ 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_MEMBERS(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_EMPTY(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 +743,17 @@ 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_MEMBERS(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_EMPTY(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 +764,15 @@ 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_MEMBERS(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__)) })

+// identical to NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY: with no members there is nothing to default
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_EMPTY(Type, BaseType) NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY(Type, BaseType)
+
+#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 +783,14 @@ 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_MEMBERS(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_EMPTY(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 +801,17 @@ 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_MEMBERS(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_EMPTY(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 +822,15 @@ 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_MEMBERS(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__)) })

+// identical to NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY: with no members there is nothing to default
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_EMPTY(Type, BaseType) NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY(Type, BaseType)
+
+#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 +841,14 @@ 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_MEMBERS(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_EMPTY(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__)) })

@@ -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 EMPTY when
+// __VA_ARGS__ is a single token (Type alone) and to MEMBERS for two or more
+// (Type, member...), naming the body the public macro dispatches to. It
+// reuses 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.
+//
+// NLOHMANN_JSON_DERIVED_TYPE_TAG(...) answers the same question for the
+// derived-type macros, whose fixed prefix is Type,BaseType. It drops the
+// leading Type and defers to NLOHMANN_JSON_TYPE_TAG rather than shifting the
+// slot table by one: NLOHMANN_JSON_GET_MACRO only resolves 64 positional
+// arguments, so tagging Type,BaseType,member... directly would run out one
+// slot early and cap the derived-type macros at 62 members instead of the 63
+// that NLOHMANN_JSON_PASTE supports.
+#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__, \
+        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
+        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
+        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
+        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
+        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
+        MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, MEMBERS, \
+        MEMBERS, MEMBERS, MEMBERS, EMPTY, \
+        NLOHMANN_JSON_TYPE_TAG_SENTINEL))
+
+#define NLOHMANN_JSON_DERIVED_TYPE_TAG_(Type, ...) NLOHMANN_JSON_TYPE_TAG(__VA_ARGS__)
+#define NLOHMANN_JSON_DERIVED_TYPE_TAG(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DERIVED_TYPE_TAG_(__VA_ARGS__))
+
 /*!
@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_MEMBERS(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_EMPTY(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 +3025,15 @@ 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_MEMBERS(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__)) })

+// identical to NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY: with no members there is nothing to default
+#define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_EMPTY(Type) NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY(Type)
+
+#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 +3044,14 @@ 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_MEMBERS(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_EMPTY(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 +3061,17 @@ 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_MEMBERS(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_EMPTY(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 +3082,15 @@ 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_MEMBERS(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__)) })

+// identical to NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY: with no members there is nothing to default
+#define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_EMPTY(Type) NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY(Type)
+
+#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 +3101,14 @@ 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_MEMBERS(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_EMPTY(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 +3118,17 @@ 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_MEMBERS(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_EMPTY(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 +3139,15 @@ 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_MEMBERS(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__)) })

+// identical to NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY: with no members there is nothing to default
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_EMPTY(Type, BaseType) NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY(Type, BaseType)
+
+#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 +3158,14 @@ 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_MEMBERS(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_EMPTY(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 +3176,17 @@ 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_MEMBERS(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_EMPTY(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 +3197,15 @@ 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_MEMBERS(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__)) })

+// identical to NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY: with no members there is nothing to default
+#define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_EMPTY(Type, BaseType) NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY(Type, BaseType)
+
+#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 +3216,14 @@ 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_MEMBERS(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_EMPTY(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__)) })

@@ -778,6 +778,154 @@ 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)
+
+// Types at the documented maximum member count (63) for issue #4041's
+// argument-count dispatch. The derived-type macros carry a two-token
+// Type,BaseType prefix, so they reach two slots further into
+// NLOHMANN_JSON_GET_MACRO than the non-derived ones and are the first to break
+// if the tag dispatch runs out of positional slots.
+class max_members
+{
+  public:
+    int m1{}, m2{}, m3{}, m4{}, m5{}, m6{}, m7{}, m8{}, m9{}, m10{}, m11{}, m12{}, m13{}, m14{}, m15{}, m16{}, m17{}, m18{}, m19{}, m20{}, m21{}, m22{}, m23{}, m24{}, m25{}, m26{}, m27{}, m28{}, m29{}, m30{}, m31{}, m32{}, m33{}, m34{}, m35{}, m36{}, m37{}, m38{}, m39{}, m40{}, m41{}, m42{}, m43{}, m44{}, m45{}, m46{}, m47{}, m48{}, m49{}, m50{}, m51{}, m52{}, m53{}, m54{}, m55{}, m56{}, m57{}, m58{}, m59{}, m60{}, m61{}, m62{}, m63{};
+
+    NLOHMANN_DEFINE_TYPE_INTRUSIVE(max_members, m1, m2, m3, m4, m5, m6, m7, m8, m9, m10, m11, m12, m13, m14, m15, m16, m17, m18, m19, m20, m21, m22, m23, m24, m25, m26, m27, m28, m29, m30, m31, m32, m33, m34, m35, m36, m37, m38, m39, m40, m41, m42, m43, m44, m45, m46, m47, m48, m49, m50, m51, m52, m53, m54, m55, m56, m57, m58, m59, m60, m61, m62, m63)
+};
+
+class max_members_base
+{
+  public:
+    int base_value = 0;
+
+    NLOHMANN_DEFINE_TYPE_INTRUSIVE(max_members_base, base_value)
+};
+
+class max_members_derived : public max_members_base
+{
+  public:
+    int m1{}, m2{}, m3{}, m4{}, m5{}, m6{}, m7{}, m8{}, m9{}, m10{}, m11{}, m12{}, m13{}, m14{}, m15{}, m16{}, m17{}, m18{}, m19{}, m20{}, m21{}, m22{}, m23{}, m24{}, m25{}, m26{}, m27{}, m28{}, m29{}, m30{}, m31{}, m32{}, m33{}, m34{}, m35{}, m36{}, m37{}, m38{}, m39{}, m40{}, m41{}, m42{}, m43{}, m44{}, m45{}, m46{}, m47{}, m48{}, m49{}, m50{}, m51{}, m52{}, m53{}, m54{}, m55{}, m56{}, m57{}, m58{}, m59{}, m60{}, m61{}, m62{}, m63{};
+
+    NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(max_members_derived, max_members_base, m1, m2, m3, m4, m5, m6, m7, m8, m9, m10, m11, m12, m13, m14, m15, m16, m17, m18, m19, m20, m21, m22, m23, m24, m25, m26, m27, m28, m29, m30, m31, m32, m33, m34, m35, m36, m37, m38, m39, m40, m41, m42, m43, m44, m45, m46, m47, m48, m49, m50, m51, m52, m53, m54, m55, m56, m57, m58, m59, m60, m61, m62, m63)
+};
+
+
 } // 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 +1339,141 @@ 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);
+    }
+}
+
+// Regression test for the argument-count dispatch added for issue #4041: the
+// documented maximum of 63 members must keep working, including for the
+// derived-type macros whose Type,BaseType prefix consumes two dispatch slots.
+TEST_CASE_TEMPLATE("Serialization/deserialization of maximum-member-count types via NLOHMANN_DEFINE_TYPE_*", Json, // NOLINT(readability-math-missing-parentheses, bugprone-throwing-static-initialization)
+                   nlohmann::json, nlohmann::ordered_json)
+{
+    SECTION("NLOHMANN_DEFINE_TYPE_INTRUSIVE with 63 members")
+    {
+        persons::max_members obj{};
+        obj.m1 = 1;
+        obj.m63 = 63;
+        Json j = obj;
+        CHECK(j.size() == 63);
+        const auto obj2 = j.template get<persons::max_members>();
+        CHECK(obj2.m1 == 1);
+        CHECK(obj2.m63 == 63);
+    }
+
+    SECTION("NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE with 63 own members")
+    {
+        persons::max_members_derived obj{};
+        obj.base_value = 7;
+        obj.m1 = 1;
+        obj.m63 = 63;
+        Json j = obj;
+        CHECK(j.size() == 64);
+        const auto obj2 = j.template get<persons::max_members_derived>();
+        CHECK(obj2.base_value == 7);
+        CHECK(obj2.m1 == 1);
+        CHECK(obj2.m63 == 63);
+    }
+}
Author	SHA1	Message	Date
Niels Lohmann	f8a0990582	Document zero-member support in the macro API reference docs/mkdocs/docs/features/arbitrary_types.md already gained a note, but the three api/macros pages are where the parameter contract is actually specified and they still described member as a non-empty list. State that the list may be empty on each page, and add a note showing what the zero-member case generates: an empty JSON object for the plain macros, and base-type-only serialization for the derived ones. Both notes record that the WITH_NAMES variants do not support this. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-08-20 09:01:11 +02:00
Niels Lohmann	7e87e5920f	Name the zero-member macro bodies by intent, not argument count The dispatch tag was the literal token 1 or N, pasted onto a macro prefix to select the zero-member or member-carrying body. For the derived-type macros that reads wrong: their tag is computed after dropping the leading Type, so the zero-member body was named _1 while taking two parameters (Type, BaseType). Emit EMPTY and MEMBERS instead. The mechanism is unchanged -- the tag is still a token pasted onto the prefix by NLOHMANN_JSON_CAT -- but the body names now say what they are rather than encoding an argument count that only lines up for half of the macros. Collapse the four duplicated zero-member bodies while here: with no members there is nothing to default, so each _WITH_DEFAULT_EMPTY body was a byte-for-byte copy of its plain counterpart. They are now one-line aliases, leaving a single definition of what an empty object serializes to per intrusive/non-intrusive and base/derived combination. No functional change: for both zero-member and member-carrying types the preprocessed to_json/from_json output is token-for-token identical, and the arity limits are unchanged (63 members, base and derived). Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-08-19 23:05:45 +02:00
Niels Lohmann	0b28c63bad	Fix derived-type macro dispatch capping members at 62 instead of 63 NLOHMANN_JSON_GET_MACRO resolves 64 positional arguments, with NAME at position 65. NLOHMANN_JSON_TYPE_TAG dispatches on Type plus the member list, so it resolves correctly up to the 63 members NLOHMANN_JSON_PASTE supports. NLOHMANN_JSON_DERIVED_TYPE_TAG dispatched on the two-token Type,BaseType prefix plus the member list, running out one slot early: at 63 members, position 65 landed on the last member name instead of a sentinel and NLOHMANN_JSON_CAT built an undefined identifier such as NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_m63, with the compiler reporting "unknown type name 'm1'" once per member and nothing pointing at an argument-count limit. That silently reduced all six NLOHMANN_DEFINE_DERIVED_TYPE_* macros from 63 members to 62, contradicting the "up to 63 members" contract in docs/mkdocs/docs/api/macros/nlohmann_define_derived_type.md. Drop the leading Type and defer to NLOHMANN_JSON_TYPE_TAG so the tag is computed from BaseType plus the member list, which fits the available slots. The zero-own-member derived bodies are therefore selected by tag 1 rather than 2, and the sentinel table for the derived tag is no longer needed. Add a regression test at the documented maximum for both the plain and the derived macros; it fails to compile against the previous dispatch. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-08-19 21:03:08 +02:00
Niels LohmannandClaude	4dcd45b26d	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>	2026-07-12 06:37:49 +00:00
Niels Lohmann	9d83673263	Fix CI failures in zero-member NLOHMANN_DEFINE_TYPE_* macros Three issues surfaced on PR #5272's real CI that weren't caught by local testing against a narrower flag set: - GCC -Werror=noexcept: the four truly-empty from_json bodies (plain INTRUSIVE/NON_INTRUSIVE, with and without _WITH_DEFAULT) provably never throw but weren't declared noexcept; mark them noexcept explicitly. to_json and the derived-type from_json overloads are left alone since they genuinely can throw (object assignment / delegating to the base class's from_json). - clang-tidy bugprone-macro-parentheses: false positive on the same 8 zero-member bodies (Type/BaseType used purely as declarator types); suppressed with NOLINTNEXTLINE comments in the same style already used elsewhere in this file (see NLOHMANN_JSON_SERIALIZE_ENUM). - MSVC's traditional preprocessor doesn't fully expand NLOHMANN_JSON_CAT(prefix, NLOHMANN_JSON_TYPE_TAG(...))(...) in one pass, which broke a pre-existing one-member usage in unit-regression2.cpp with syntax errors. Wrap all 12 public dispatcher macros in an extra outer NLOHMANN_JSON_EXPAND(...), matching the pattern NLOHMANN_JSON_PASTE already uses for the same MSVC quirk. Re-verified against real GCC 16 and Clang at -std=c++11/14/17/20 with -pedantic -Werror -Wvariadic-macros -Wnoexcept, including the exact files that failed in CI (unit-udt_macro.cpp, unit-regression2.cpp), against both the modular headers and the re-amalgamated single header. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-07-11 23:55:43 +02:00
Niels Lohmann	d969eef216	Support zero-member types in NLOHMANN_DEFINE_TYPE_* macros (#4041 ) NLOHMANN_DEFINE_TYPE_INTRUSIVE(Type) and its 11 sibling macros produced broken code for types with no members to serialize. Invoking a variadic macro so __VA_ARGS__ is empty is only standard-conforming since C++20, so a plain __VA_OPT__ fix (as tried in #5142) breaks every pre-C++20 build under -pedantic. Instead, make all 12 macros purely variadic and dispatch on argument count using a sentinel-padded extension of the existing NLOHMANN_JSON_GET_MACRO idiom, giving full C++11-C++26 support with no feature-test gate. Verified against real GCC 16 and Clang at -std=c++11/14/17/20 with -pedantic -Werror -Wvariadic-macros: zero regressions in the existing unit-udt_macro.cpp suite plus 12 new zero-member test cases. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-07-11 19:55:56 +02:00