D, Java? To D or not to D?

[Frits van Bommel]

Walter Bright wrote:
> TPJ wrote:
>> 1) In order to run a program written in D I have to compile it on the 
>> target OS.
> 
> I haven't talked about this much, but it is technically feasible to 
> create a D runtime that enables "compile once, run everywhere". It is 
> not necessary to have a VM to do it.

How would you implement a garbage collector in an 
architecture-independent way?

Or are you talking about using version(arch_1) to version(arch_N)? [1]
Because I'm pretty sure the garbage collector has to know some 
architecture-specific things. Start of stack, direction of stack, 
location of static data, threading API (if any), that sort of thing.
So you'd need to perform at least _some_ porting to get it to run on a 
new architecture, if only to tell the GC what its properties are.

Though I guess stack direction could be experimentally determined at 
runtime/install time, as could endianness... Threading API is going to 
be hard to determine in that way, I'd think.


[1] or "version(StackGrowsUp), version(BigEndian), version(HasFeatureX), 
version(HasFeatureY), ..." or something like that.