Want reasonable reference counting? Disable automatic sharing of immutable

[Imperatorn]

On Friday, 12 November 2021 at 12:31:03 UTC, Steven Schveighoffer 
wrote:
> One of the prerequisites to doing reference counting is to have 
> a mutable piece of data inside an immutable piece of data.
>
> [...]

Just putting this here for reference (regarding implicitly shared 
immutable)

![Quadrants](https://image.slidesharecdn.com/refactoringtoimmutability-180703134457/95/refactoring-to-immutability-24-638.jpg "Immutable-shared")