Unexpected behaviour of is_null

[phyz777]

The following code produces unexpected output (which is, all four statements being printed):

#include <iostream>

#include "json.hpp"

int main()
{
    nlohmann::json j;

    if (j.empty()) {
        std::cout << "Object is empty" << std::endl;
    }

    if (j.is_null()) {
        std::cout << "Object is null" << std::endl;
    }

    nlohmann::json k;

    j["aminull"] = k;

    if (j["aminull"].empty()) {
        std::cout << "Object under key is empty" << std::endl;
    }

    if (j["aminull"].is_null()) {
        std::cout << "Object under key is null" << std::endl;
    }

    return 0;
}

I am not entirely sure whether or not this is the expected behaviour, but I think it would be more intuitive to have only the empty() conditions evaluate to true and the others to false?

Best wishes and thanks for the great work!

[phyz777]

By the way, the following works as expected:

    nlohmann::json l = nlohmann::json::object();

    if (l.empty()) {
        std::cout << "Object is also empty" << std::endl;
    }

    if (l.is_null()) {
        std::cout << "Object is also null" << std::endl;
    }

If all of this is intended to work like this: sorry for the hassle and please, feel free to silently delete this issue.

[nlohmann]

Please note:

• Uninitialized JSON values are null by default.
• empty() returns true if and only if size() == 0.
• null values have the size 0, because they have no value (see documentation).
• objects/arrays are empty if they have no entries.

In your second example, I do not believe that l.is_null() is true.

[phyz777]

Yes, indeed, is_null does not evaluate to true here, this is what I meant with 'works as expected'.
Well, in this case, everything is just fine. Feel free to delete or close this issue. (:

[nlohmann]

No worries - every ticket may be helpful for others and give me an idea what needs to be documented more thoroughly.