Using closure in function scope to make "real" private class members

[zjh]

On Wednesday, 8 June 2022 at 09:38:24 UTC, Ola Fosheim Grøstad 
wrote:
  but then there
> would be many such adjustments to make.
>
> To make all those adjustments in D2 with no breaking change 
> would @lead @to @a @mess.

Will it be so `troublesome` if it is `well encapsulation`?