While trying to make a simple array, I get a nested array instead

[jlconlin]

• Describe what you want to achieve.
  I'm trying to make a simple JSON array for my custom class

• Describe what you tried.

struct A{
  int c1;
  int c2;
};

void to_json( json& JSON, const A& a ){
  JSON = { A.c1, A.c2 };
}

A myA{ 21, 22};

auto json = nlohmann::json{ myA };
// Gives me [[ 21, 22]]
// Would like it to return [21, 22]

I've also tried (from #1013)

void to_json( json& JSON, const A& a ){
  JSON = std::forward_list< int >{ A.c1, A.c2 };
}

and got the same response.

• Describe which system (OS, compiler) you are using.
  MacOS 10.14, LLVM 3.8

• Describe which version of the library you are using (release version, develop branch).
  master branch, commit c0d511ea500e698061a4b288bd77ce43bd76fa70 (okay, it's kind of old)

[nlohmann]

The library interprets the braces in

auto json = nlohmann::json{ myA };

as array. Try replacing this by

nlohmann::json json = myA;

[jlconlin]

This works, but I'm struggling to understand the difference. Why aren't the braces interpreted as brace initialization?

[nlohmann]

I think it is interpreted as an initializer list, and the corresponding (implicit) constructor creates an array.