Null references redux + Cyclone

[Jeremie Pelletier]

bearophile wrote:
> Walter Bright:
> 
>> No, it is done with one indirection.<
> 
> If even Andrei, a quite intelligent person that has written big books on C++, may be wrong on such a basic thing, then I think there's a problem.
> 
> It can be good to create an html page that explains how some basic things of D are implemented in the front-end. Such page can also contain box & arrow images that show how structures and memory are organized for various of such data structures.
> 
> Such html page is useful for both normal programmers that want to understand what's under the hood, and for people that may want to fix/modify the front-end.
> 
> Bye,
> bearophile

I agree, the ABI documentation on digitalmars.com is far from complete, 
I had to learn a lot of it through trial and error. What was especially 
confusing was the interface reference vs the interface info vs the 
interface's classinfo vs the referenced object, I wrote an internal 
wrapper struct to make most of the casts go away:

struct Interface {
	Object object() const {
		return cast(Object)(cast(void*)&this - interfaceinfo.offset);
	}

	immutable(InterfaceInfo)* interfaceinfo() const {
		return **cast(InterfaceInfo***)&this;
	}

	immutable(ClassInfo) classinfo() const {
		return interfaceinfo.classinfo;
	}
}

immutable struct InterfaceInfo {
	ClassInfo			classinfo;
	void*[]				vtbl;
	ptrdiff_t			offset;
}

These two made implementing D internals a whole lot easier! I think only 
InterfaceInfo is in druntime (and its confusingly named Interface in there).