add strict enum de/serialization macro by hnampally · Pull Request #4612 · nlohmann/json

hnampally · 2025-01-20T04:53:58Z

#3992

The changes are described in detail, both the what and why.
If applicable, an #3992 is referenced.
The Code coverage remained at 100%. A test case for every new line of code.
If applicable, the documentation is updated.
The source code is amalgamated by running make amalgamate.

Read the Contribution Guidelines for detailed information.

Signed-off-by: Harinath Nampally <harinath922@gmail.com>

github-actions · 2025-01-20T04:56:45Z

🔴 Amalgamation check failed! 🔴

The source code has not been amalgamated. @hnampally
Please read and follow the Contribution Guidelines.

coveralls · 2025-01-20T05:25:14Z

coverage: 99.186%. remained the same
when pulling 6747555 on hnampally:issue-3992
into 606b634 on nlohmann:develop.

Signed-off-by: Harinath Nampally <harinath922@gmail.com>

github-actions · 2025-01-26T22:03:23Z

🔴 Amalgamation check failed! 🔴

The source code has not been amalgamated. @hnampally
Please read and follow the Contribution Guidelines.

Signed-off-by: Harinath Nampally <harinath922@gmail.com>

nlohmann · 2025-01-27T06:45:30Z

+template<typename T>
+[[noreturn]] inline void json_throw_from_serialize_macro(T&& exception)
+{
+#if defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND) || defined(EXCEPTIONS)


When defining JSON_THROW in the same file, we use the following code to detect exceptions. Please use the same here to avoid issues.

#if (defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND)) && !defined(JSON_NOEXCEPTION)

oh okay, thanks!

nlohmann · 2025-01-27T06:49:56Z

+        });                                                                                     \
+        if (it == std::end(m)) { \
+            auto value = static_cast<typename std::underlying_type<ENUM_TYPE>::type>(e); \
+            nlohmann::detail::json_throw_from_serialize_macro(nlohmann::detail::type_error::create(302, nlohmann::detail::concat("can't serialize - enum value ", std::to_string(value), " out of range"), &j)); \


I don't like the exception message. What about

serialization failed: enum value ... is out of range

Yes that sounds better, thanks!

nlohmann · 2025-01-27T06:52:01Z

+            return ej_pair.second == j;                                                         \
+        });                                                                                     \
+        if (it == std::end(m))            \
+            nlohmann::detail::json_throw_from_serialize_macro(nlohmann::detail::type_error::create(302, nlohmann::detail::concat("can't deserialize - invalid json value : ", j.dump()), &j)); \


Same as above:

deserialization failed: invalid JSON value '...'

Signed-off-by: Harinath Nampally <harinath922@gmail.com>

gregmarr · 2025-01-28T03:28:58Z

+
+    - If an enum value appears more than once in the mapping, only the first occurrence will be used for serialization, 
+        subsequent mappings for the same enum value will be ignored.
+    - If a JSON value appears more than once in the mapping, only the first occurrence will be used for deserialization, 


"If a string value" since it's not an arbitrary json value but a string....

Oh, OH, it doesn't require that it be a string, does it?

😮

There's nothing in the code that requires that this be a string.

NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(Color, { { Red, "red" }, { Green, nlohmann::json(1) }, { Blue, nlohmann::json({{{"purple", "people eater"}}})} }) int main() { nlohmann::json j; j = { Red, Green, Blue }; std::cout << j.dump() << "\n"; auto j2 = nlohmann::json::parse(j.dump()); std::vector<Color> vec = j2; std::cout << vec[0] << vec[1] << vec[2]; }

["red",1,[{"purple":"people eater"}]] 012

@hnampally Is this intended behavior, or did this just accidentally fall out of the second parameter being BasicJsonType instead of std::string?

If this is intended behavior, it should definitely be documented before someone trips upon it accidentally, or someone relies on it and then someone else "fixes" it.

If it's not intended behavior, then it should be fixed.

Signed-off-by: Harinath Nampally <harinath922@gmail.com>

nlohmann · 2025-01-31T15:51:40Z

+    Expected output:
+
+    ```
+    [json.exception.type_error.302] serialization failed: enum value 3 is out of range


Also use an include here:

--8<-- "examples/nlohmann_json_serialize_enum_strict.output"

nlohmann · 2025-01-31T15:52:15Z

+    Expected output:
+
+    ```
+    [json.exception.type_error.302] deserialization failed: invalid JSON value "yellow"


Also use an include here:

--8<-- "examples/nlohmann_json_deserialize_enum_strict.output"

nlohmann · 2025-01-31T15:53:34Z

+
+int main()
+{
+


Remove the empty line.

Also: move line

json j_yellow = "yellow";

above the comment

// deserialization

gregmarr · 2025-01-31T17:59:48Z

It looks like you have a space in your filename here:
docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum _strict.md

Also, the discussion about strings vs arbitrary json for the value has been marked outdated because there was a change in the file. @nlohmann did you see that discussion?

Signed-off-by: Harinath Nampally <harinath922@gmail.com>

jmonticelli · 2025-04-01T19:53:58Z

This looks particularly useful, I was surprised by the behavior of the default enum serialization macro.
Thanks for putting this PR up btw @hnampally

github-actions · 2026-05-11T00:32:59Z

This pull request has been marked as stale because it has had no activity for 30 days. While we won’t close it automatically, we encourage you to update or comment if it is still relevant. Keeping pull requests active and up-to-date helps us review and merge changes more efficiently. Thank you for your contributions!

nlohmann · 2026-05-17T15:36:09Z

@hnampally I know it's been a while, but would you be willing to pick this up again?

hnampally · 2026-05-17T18:14:06Z

@hnampally I know it's been a while, but would you be willing to pick this up again?

@nlohmann Sure, let me give this PR a quick re-read and hopefully we can get it merged/closed.

gregmarr · 2026-05-18T15:00:54Z

@nlohmann Isn't this the same thing as #5151 which is just about ready to go?

hnampally · 2026-05-18T15:13:30Z

#5151 solves the same issue and ready to go, therefore cloing this PR

nlohmann · 2026-05-18T18:37:46Z

@hnampally Sorry for the confusion!

hnampally requested a review from nlohmann as a code owner January 20, 2025 04:53

github-actions Bot added documentation L tests labels Jan 20, 2025

add strict enum de/serialization macro

06b667c

Signed-off-by: Harinath Nampally <harinath922@gmail.com>

hnampally force-pushed the issue-3992 branch from 0f7ec10 to 06b667c Compare January 20, 2025 04:56

hnampally added 3 commits January 20, 2025 00:40

fix ci checks

4ebebad

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fix few more ci checks

0083937

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fix typos

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Comment thread docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum _strict.md Outdated

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hnampally added 3 commits January 25, 2025 09:31

address review comment

4444985

Signed-off-by: Harinath Nampally <harinath922@gmail.com>

fix ununsed variable static check

e7c021f

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ci static check fix

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hnampally force-pushed the issue-3992 branch from 9dd05aa to e17bf40 Compare January 26, 2025 22:03

hnampally force-pushed the issue-3992 branch from e17bf40 to c2d0b8b Compare January 26, 2025 22:17

address review comment

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hnampally force-pushed the issue-3992 branch from c2d0b8b to 2898659 Compare January 26, 2025 22:21

gregmarr reviewed Jan 26, 2025

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address review comments

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hnampally force-pushed the issue-3992 branch from 4002093 to ba344e0 Compare January 26, 2025 23:38

fix ci check

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hnampally force-pushed the issue-3992 branch from ba344e0 to 0cda972 Compare January 27, 2025 02:24

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hnampally force-pushed the issue-3992 branch from 3a55919 to e25fc04 Compare January 28, 2025 02:49

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further documentation improvements

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hnampally force-pushed the issue-3992 branch from 00990b1 to 5f7d41c Compare January 29, 2025 03:04

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6747555

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hnampally requested a review from nlohmann February 4, 2025 04:55

github-actions Bot added the state: stale the issue has not been updated in a while and will be closed automatically soon unless it is updated label May 11, 2026

github-actions Bot removed the state: stale the issue has not been updated in a while and will be closed automatically soon unless it is updated label May 18, 2026

hnampally closed this May 18, 2026

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