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

[Elronnd]

On Tuesday, 14 December 2021 at 06:27:27 UTC, Elronnd wrote:
> I think it would be reasonable to define provenance semantics 
> which permit you to derive a mutable pointer from an immutable 
> one

Simple example:

struct S { immutable float x; int y; }
S a;
immutable float* x = &a.x;
int y = *cast(int*)(cast(ubyte*)&x + (S.y.offsetof - 
S.x.offsetof))

above should be UB if (cast(ubyte*)&x + (S.y.offsetof - 
S.x.offsetof)) does not actually point to mutable memory.  This 
is subtly different from:

int x;
const int *p = &x;
*cast(int*)p = 5;

but still similar enough to warrant concern; which is why I think 
it would also be reasonable to make the former form illegal.