Generic flatten (2d and 3d)

[milancurcic]

I attempted to make a generic flatten so that the user doesn't need to do flatten2d. It seems like it will work.

In support of Linear2d (#197)

[ricor07]

LGTM

[OneAdder]

Yep, I thought about that but decided not to make the code even less SOLID

[OneAdder]

But here we have a choice between SOLID and less boilerplate, I think I agree that the second one is better

[milancurcic]

Yes, and, most importantly for me, this approach allows for a unified API (only one flatten() for the user).

[OneAdder]

Perhaps, just make it one method with assumed-rank input?

  pure module subroutine forward(self, input)
    class(flatten_layer), intent(in out) :: self
    real, intent(in) :: input(..)
    select rank(input)
      rank(2)
        self % output = pack(input, .true.)
      rank(3)
        self % output = pack(input, .true.)
      rank default
        error stop "Unsupported rank of input"
    end select
  end subroutine forward

It will reduce boilerplate a little

[milancurcic]

Cool! If it works, let's do it.

[OneAdder]

done

[OneAdder]

Thank you! I'll rebase and test it out!

[OneAdder]

Everything works. Great job!