tuple_size<>::value and 'private' keyword about pfr

[apolukhin]

Tried to do my best with private/protected. If you'll find a better way to deal with the problem, or some more missing static_asserts - please give me a hint!

Great thanks for the error report and for the code snippet.

[mdimura]

Answer my own question:

C++17 limitations: T must be aggregate initializable

An aggregate is an array or a class (Clause 9) with no user-provided constructors (12.1), no brace-or-equal-initializers for non-static data members (9.2), no private or protected non-static data members (Clause 11), no base classes (Clause 10), and no virtual functions (10.3).

[apolukhin]

Actually this seems to be an error.

I have to improve library internals to provide a compile time assert with a string like "Provided type is not an aggregate: private members are not allowed."