Re: [Swarm-Modelling] Floating point arithmetic

[Marcus G. Daniels]

Paul Johnson wrote:

> I have wondered what a C++ program of that sort would look like.  Do 
> you have any working example?

Hmm, I had some, but it seems SFI lost the old Swarm CVS tree.   (The 
machine crashed and they haven't found any backups.)

The COM support is in the normal Swarm source tree, though.  It requires 
a Mozilla or Firefox build for the XPCOM infrastructure.   I think it 
would be relatively easy to adapt to Microsoft .NET, but I never tried.  
COM or XPCOM (a.k.a. Cross Platform COM) is essentially a C++ interface, 
but one that follows certain conventions to facilitate interoperability 
with other languages.  For example XPCOM interfaces can be called by 
Python and JavaScript in the Firefox web browser.

> I'm wondering, for example, is there a ModelSwarm.m from Obj-C and 
> then a C++ file Agent.cc that somehow get put together?  Or is it like 
> the JNI interface, where it is all in Java and then the OBJC classes 
> get linked in?

The latter.  The Swarm C++ user imports C++ headers (not Objective C 
headers).   The user then links against a C++ version of the Swarm 
library which in turn links against the Swarm kernel.  It's basically 
just like the Objective C Swarm workflow (Makefiles and so on), but 
instead of calling the Objective C compiler it calls the C++ compiler.

The only sense in which Objective C is exposed is in the sense that 
there is the possibility (but not the necessity), of messages 
disembodied from classses; there is a class for Selectors.   So the C++ 
user doesn't need to know about Objective C notions unless they want to 
use dynamic method invocation from the Swarm scheduler.   (They can also 
use fixed class targets with methods that are known to work.)

The headers are generated from the abstract description of Swarm 
interfaces, namely the Swarm Objective C protocol files (just as it is 
for the Swarm documentation and Java layer).  The C++ implementation is 
also generated, but all the implementation does is the object 
conversions as is done for the JNI layer.   These techniques were 
reasonably well-optimized for Java, and COM inherits most of that.