Are D classes proper reference types?

[kinke]

On Saturday, 26 June 2021 at 13:49:25 UTC, Ola Fosheim Grøstad 
wrote:
> Is it possible to inherit from a C++ class and get a D 
> subclass, and is it possible to inherit from a D class and get 
> a C++ class?

Sure thing, with `extern(C++) class` of course.

> But the best solution is to get to a place where you can hand 
> D-objects to other languages with ease without doing a runtime 
> conversion from one layout to another.

With C++, you can today, an `extern(C++) class C` is equivalent 
to and mangled as C++ `C*`. You can't pass it directly to some 
`unique_ptr<C>` or `shared_ptr<T>` of course; an according D 
wrapper reflecting the C++ implementation (library-dependent) 
would be needed anyway for correct mangling. It'd be implemented 
as a templated D struct, similar to how `std::vector` works today 
for the MSVC runtime: 
https://github.com/dlang/druntime/blob/master/src/core/stdcpp/vector.d