D, Java? To D or not to D?

[Don Clugston]

Georg Wrede wrote:
> 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.
> 
> 1. To run on any OS on one specific processor, either those OSes have to 
> have different entry points to the "exe", or there has to be a way of 
> probing the OS within "common" code, the result of which would cause a 
> jump to an OS specific routine.
> 
> 2. To run on different processor architectures, (most probably with some 
> of the same OSes), the worst case scenario would be that the same OS 
> with the same jump target gets invocated on a different processor. This 
> would mean that one (er, Walter) would have to invent a series of binary 
> instructions that would not cause an (unwanted) exception on any of the 
> processors, would not have any harmful side effects, and would 
> eventually result in a jump to some processor specific version of the code.

> At first sight ("hearing" ?), it sounds too good to be true. Then one 
> starts to suspect that either Walter has figured out a runtime gimmick 
> that does it (thus rendering this (btw, patentable idea) independent of 
> D), or it is some kind of result of the specific way D and its source 
> code (more to the point, syntax domain) relate to the semantics of the 
> source code, taken as a whole.

I've come up with one vague idea about how this could be done (which 
doesn't involve either 1 or 2), though it would involve an obscene hack, 
telling some serious lies to the OS. I can't think of a way it could be 
done for OSes with radically different file formats, though.