Class instance memory overhead lower than 3 words?

[kinke]

On Wednesday, 24 January 2018 at 21:48:21 UTC, Nordlöw wrote:
> Why is the memory overhead for a class instance as high as 3 
> words (24 bytes on 64-bit systems? I find that annoyingly much 
> for my knowledge database application. I'm aware of 
> extern(C++), having one word overhead, but such 
> extern(C++)-classes cannot use all of D; I get compilation 
> errors such as
>
> node.d(99,25): Error: Internal Compiler Error: type 
> `inout(Edge)[]` can not be mapped to C++

If you don't need C++ interop and only care about getting rid of 
the monitor pointer, you can declare the class as C++ class but 
use the D linkage/ABI for all functions, so that they accept D 
slices:

extern(C++) class Node
{
     extern(D):
     void foo(Node[] nodes) {}
}

Is a struct not an option?