Challenge: write a reference counted slice that works as much as possible like a built-in slice

[Elronnd]

On Monday, 8 November 2021 at 21:42:12 UTC, Andrei Alexandrescu 
wrote:
> 1. We could not make reference counting work properly in pure 
> functions (a pure function does not mutate data, which goes 
> against manipulating the reference count).

pure functions can mutate data passed to them.  And for a struct 
method (such as a copy constructor) this includes the struct's 
fields.