Json should not be constructible with 'json*'

I had something like this:

        json* p;
        json j(p);

This was a bug (I need to dereference the pointer), but json constructor accepts it as a boolean type because it's finding this overload:

template<typename BasicJsonType>
void to_json(BasicJsonType& j, typename BasicJsonType::boolean_t b) noexcept

The problem with 'bool' is that it captures a lot of things. Classes with 'operator bool()' are also being caught.

I can think of some simple changes (SFINAE something), but I'm not sure how well they work with arbitrary BasicJsonType's.

Maybe the default to_/from_json should be implemented just for the common C++ types (bool, std::string, std::map, std::vector) and not in terms of BasicJson::whatever_t, and if you specialize basic_json then you have to also manually opt-in to the right to_/from_json overloads?

If I remember correctly, there was a constructor for each BasicJsonType:: whatever _t prior to 2.1.0.

So I think we should keep those overloads for now, to keep backward compatibility.

To avoid this implicit conversion, I guess a simple std::is_same<typename BasicJsonType::boolean_t, T> in the enable_if will do the trick. It would be great to fix similar issues with different parameter types (integers and so on)

Unfortunately I don't have a laptop at hand until Sunday to test this

@theodelrieu

@theodelrieu I agree in both points, and I think I won't have time to fix this this week either.

I have done this and it seems to work:

-template<typename BasicJsonType>
-void to_json(BasicJsonType& j, typename BasicJsonType::boolean_t b) noexcept
+template<typename BasicJsonType, typename T,
+    enable_if_t<std::is_same<std::decay_t<T>, typename BasicJsonType::boolean_t>::value, int> = 0>
+void to_json(BasicJsonType& j, T b) noexcept

I'm not 100% that the decay is necessary.

🚑 fix for #448

@jaredgrubb

Fixed using @jaredgrubb 's proposal.

I don't think the decay is useful, but that's a minor thing.

Thanks for the fix!

I shall remove the decay then.

🚧 removed decay (#448)

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Json should not be constructible with 'json*' #448

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Json should not be constructible with 'json*' #448

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jaredgrubb commented on Feb 12, 2017

theodelrieu commented on Feb 13, 2017

nlohmann commented on Feb 13, 2017

jaredgrubb commented on Feb 14, 2017

nlohmann commented on Feb 19, 2017

theodelrieu commented on Feb 20, 2017

nlohmann commented on Feb 20, 2017

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