Are D classes proper reference types?

[kinke]

On Friday, 25 June 2021 at 17:05:41 UTC, Ola Fosheim Grøstad 
wrote:
> Yes, if you don't want to support weak pointers. I think you 
> need two counters if you want to enable the usage of weak 
> pointers.

I cannot imagine how weak pointers would work without an ugly 
extra indirection layer. If we're on the same page, we're talking 
about embedding the reference counter *directly* in the class 
instance, and the class ref still pointing directly to the 
instance.

Weak pointers aren't in the language, so I don't see why they 
would matter here. I thought you were after replacing 
GC-allocated class instances by a simple RC scheme.

> One reason to put it at a negative offset is that it makes it 
> possible to make it fully compatible with shared_ptr.

In modern C++ code I've been looking at so far, shared_ptr was 
used very rarely (and unique_ptr everywhere). AFAIK, the main 
reason being poor performance due to the extra indirection of 
shared_ptr. So replacing every D class ref by a 
shared_ptr-analogon for interop reasons would seem very backwards 
to me.