Change `operator==` overload that constrains to `is_scalar_v` to constrain to compatible types. #4181

fsandhei · 2023-10-08T11:36:45Z

#4165 shows an issue with the overload resolution when attempting to compare a std::string with json from left to right. This can be fixed by changing the constraint to instead of focusing on scalar types, we constrain the comparison operator to "compatible types", in par with the catch-call constructor.

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Changes are described in the pull request, or an existing issue is referenced.
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The source code is amalgamated; that is, after making changes to the sources in the include/nlohmann directory, run make amalgamate to create the single-header files single_include/nlohmann/json.hpp and single_include/nlohmann/json_fwd.hpp. The whole process is described here.

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…atible types.

github-actions · 2023-10-08T11:58:01Z

🔴 Amalgamation check failed! 🔴

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

github-actions · 2023-10-08T12:35:48Z

🔴 Amalgamation check failed! 🔴

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

coveralls · 2023-10-08T12:41:35Z

coverage: 100.0%. remained the same
when pulling 65b9b38 on fsandhei:fix/equality-operator-for-compatible-types
into 0457de2 on nlohmann:develop.

nlohmann · 2023-10-09T07:18:55Z

Can you please try to amalgamate with an older version of astyle, like astyle 3.2? There was a breaking change in astyle which makes the output differ unfortunately.

fsandhei · 2023-10-09T10:19:26Z

Can you please try to amalgamate with an older version of astyle, like astyle 3.2? There was a breaking change in astyle which makes the output differ unfortunately.

Sure, I'll do it some time later today after work.

There seems to be some issues or inconsistencies with the astyle version 3.2.1 from the AUR versus 3.2.1-build from apt: * --squeeze-lines is not defined in the one from Arch, so I had to comment that one out in order to make the amalgamate step run. * A bunch of files are affected by the amalgamate, which does not seem right.

fsandhei · 2023-10-09T16:37:14Z

First, sorry, @nlohmann, for the trouble I'm causing here.

So, I tried amalgamating again. There seems to be some issues or inconsistencies with the astyle version 3.2.1 from the AUR versus 3.2.1-build from apt:

--squeeze-lines is not defined in the one from Arch, so I had to
comment that one out in order to make the amalgamate step run.
As far as I see, squeeze-line was introduced in 3.3.x.
A bunch of files are affected by the amalgamate, which does not
seem right.

Would you want me to perhaps unstage all the other unrelated files that got affected by this?

github-actions · 2023-10-09T18:25:52Z

🔴 Amalgamation check failed! 🔴

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

This reverts commit ca40711.

nlohmann · 2023-10-09T18:52:05Z

This is what I am using locally (patched Makefile):

# call the Artistic Style pretty printer on all source files
pretty:
	/Users/niels/Downloads/astyle/build/astyle \
	    --style=allman \
	    --indent=spaces=4 \
	    --indent-modifiers \
	    --indent-switches \
	    --indent-preproc-block \
	    --indent-preproc-define \
	    --indent-col1-comments \
	    --pad-oper \
	    --pad-header \
	    --align-pointer=type \
	    --align-reference=type \
	    --add-braces \
	    --convert-tabs \
	    --close-templates \
	    --lineend=linux \
	    --preserve-date \
	    --suffix=none \
	    --formatted \
	   $(SRCS) $(TESTS_SRCS) $(AMALGAMATED_FILE) $(AMALGAMATED_FWD_FILE) docs/examples/*.cpp

with Astyle 3.1.

fsandhei · 2023-10-09T19:49:17Z

Thank you for so quick response. The amalgamation seems happy now.

nlohmann · 2023-10-09T19:50:31Z

Thank you for so quick response. The amalgamation seems happy now.

Thanks for your effort!

Opting out of using concept and rather defining a structure while still being able to not use SFINAE and instead `requires` expression. Compiling with C++23 on GCC 13.2.1 fails on overload resolution on calling operator== for `std::nullptr_t`. The solution for this was to simply add another overload for nullptr, on par with the equivalent `nullptr_t` constructor.

fsandhei · 2023-10-11T21:37:58Z

I see that the GCC 10 CI run failed. It seems to be not able to parse the concept, which is odd as it should be supported in GCC 10.

For the sake of getting this in and have the least amount of hassle I don't use concept.

However I was pondering on the idea of having a concept which could replace these type traits definitions for recognizing "compatible types". I tinkered with this simple concept below. It worked perfectly fine. I don't know if it is missing any details, though. Would appreciate hearing your opinion on this, as I'm far from an expert :)

#ifdef JSON_HAS_CPP_20
   #include <concepts>
    template <typename T, typename BasicJsonType, typename U = uncvref_t<T>>
    concept CompatibleType = requires(const U& type, BasicJsonType& j) {
        { to_json(j, type) } -> std::convertible_to<void>;
    };
#endif

The use of this would be quite simple, as we'd then can constrict constructors / operators with this concept:

template <CompatibleType<basic_json_t> T>
operator==(T rhs) const noexcept
{
   ...
}

EDIT: I realize I goofed myself. It is supported but JSON_HAS_CPP_20 is not defined because g++10 requires -std=c++2a. I'm able to get past this by also checking for __cpp_concepts to be defined at where we define the concept.

fsandhei · 2024-02-29T21:53:39Z

I'm not really sure what is Codacy is actually complaining about. The struct member is being used in the type trait. It might be a bug in Codacy. Do you have any suggestions @nlohmann?

nlohmann · 2024-03-01T07:58:00Z

I'm not really sure what is Codacy is actually complaining about. The struct member is being used in the type trait. It might be a bug in Codacy. Do you have any suggestions @nlohmann?

Indeed looks like a false positive. I set it to "ignore".

github-actions · 2024-03-01T08:15:46Z

🔴 Amalgamation check failed! 🔴

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

fsandhei added 3 commits October 7, 2023 15:26

Replace scalar type comparison restriction with one extended for comp…

d21abfc

…atible types.

Create a concept for compatible types and use it instead of SFINAE.

1eb5d38

Run amalgamate script

4b37136

fsandhei requested a review from nlohmann as a code owner October 8, 2023 11:36

github-actions bot added L tests labels Oct 8, 2023

Add check for comparison from left to right.

828bac9

Revert "Try amalgamate again."

d4f9594

This reverts commit ca40711.

amalgamate with astyle==3.1.2

ee57287

github-actions bot added M and removed L labels Oct 9, 2023

fsandhei added 2 commits February 29, 2024 21:24

Use SFINAE instead of 'requires' clause because of cppcheck.

0c9adb1

Use bool instead of auto

b20332d

fsandhei force-pushed the fix/equality-operator-for-compatible-types branch from a2f3b70 to b20332d Compare February 29, 2024 21:53

fsandhei added 4 commits March 6, 2024 14:57

Amalgamate

7fe8dad

Fix compile errors on other versions of clang

65b9b38

Operator for non equality

fc19190

amalgamate

8d89661

Provide feedback

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Change `operator==` overload that constrains to `is_scalar_v` to constrain to compatible types. #4181

Change `operator==` overload that constrains to `is_scalar_v` to constrain to compatible types. #4181

fsandhei commented Oct 8, 2023 •

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fsandhei commented Oct 11, 2023 •

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fsandhei commented Feb 29, 2024

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github-actions bot commented Mar 1, 2024

Change operator== overload that constrains to is_scalar_v to constrain to compatible types. #4181

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Change operator== overload that constrains to is_scalar_v to constrain to compatible types. #4181

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fsandhei commented Oct 8, 2023 • edited Loading

Pull request checklist

Please don't

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Change `operator==` overload that constrains to `is_scalar_v` to constrain to compatible types. #4181

Change `operator==` overload that constrains to `is_scalar_v` to constrain to compatible types. #4181

fsandhei commented Oct 8, 2023 •

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fsandhei commented Oct 11, 2023 •

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