Error thrown when parsing in a subclass

[paulaltin]

• What is the issue you have?

When I create an instance of a subclass of nlohmann::json, attempting to deserialize a string to it using json::parse throws an error.

• Please describe the steps to reproduce the issue.

Given:

class json_subclass : public json {};

then the following all work as expected:

json a = "{}"_json;
json b(json::parse("{}"));
json c = json::parse("{}");
json d; d = json::parse("{}");

but any of the following throw an error:

json_subclass a = "{}"_json;
json_subclass b(json::parse("{}"));
json_subclass c = json::parse("{}");
json_subclass d; d = json::parse("{}");

The error thrown is [json.exception.type_error.302] type must be array, but is object.

• What is the expected behavior?

Deserializing a string to a nlohmann::json subclass should work.

• And what is the actual behavior instead?

An error is thrown: [json.exception.type_error.302] type must be array, but is object.

• Which compiler and operating system are you using?

Mac OS X 10.14.6
Xcode 11.3.1 (11C505)
Apple clang version 11.0.0 (clang-1100.0.33.17)

• Did you use a released version of the library or the version from the develop branch?

Release 3.7.3.

• Other notes

This may be related to issue #608, although I'm unable to reproduce the exact problem described there.

[paulaltin]

It works if I change the subclass definition to the following:

class json_subclass : public json
{
public:
    using json::json;
    json_subclass(const json& j) : json(j) { }
    json_subclass& operator=(const json& j) { json::operator=(j); return *this; }
};

[nlohmann]

The class is not really intended to subclass, I'm afraid.

[paulaltin]

Ok, fair enough. In that case, perhaps the class should be marked final? Or at least this could be documented in the Readme.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.