[Vm-dev] Direct pointer vs pointerForOop()

[K K Subbu]

On Saturday 07 April 2018 08:02 PM, David T. Lewis wrote:
> I have long thought that it would be a good idea for purposes of clarity
> to have a separate "sqObjectPointer" data type distinct from sqInt and
> usqInt. This would make the intentions clear, and I think it would make
> the VM code easier to read and understand. But it would probably be a
> lot of work to do this throughout the VM.

While I realize OOP is strongly entrenched in literature, terms like 
pointer, address have strong connotations of machine architecture. If 
you are going to introduce a new type, I would suggest neutral terms 
like sqObjectId, sqObjectIndex or sqObjectHandle.

How about using a union to pass them across Object and Memory layers and 
avoid all those horrid casts?

typedef union {
	u32           asId;
	void         *asAddress;
	unsigned int  asWord;
	unsigned long asLongWord;
	unsigned char asBytes[sizeof(void *)];
	...
} sqObjectId;

Object layer can access it as oop.asId and the Memory layer can use 
asWord or asAddress after suitable conversion:

sqObjectId pointerForOop(sqObjectId oop)
{return (oop.asAddress = oop.asId + sqMemoryBase, oop);}

sqObjectId oopFromPointer(sqObjectId oop)
{return (oop.asId = sqMemoryBase - oop.asAddr, oop); }

Regards .. Subbu