Method-chaining and Simple-types as objects

Daniel B. Faken faken at
Thu May 19 12:43:14 PDT 2005

On Wed, 18 May 2005, John (J5) Palmieri wrote:
> > * sending messages to simple-types (integers etc.), when they are the 
> > return-value of  a method-call.  (but see below for a more general scheme)
> But what messages would they support?

getting size, splitting, comparing, translation, hashing......

In Squeak the String class has around 200 methods, and this is not 
counting subclasses or superclasses..

> > * combining what would be multiple inter-process calls into a single one.
> Why not just do this in the API of the service?
> We throw an error if we can't marshal it to a dbus type.  In this case
> the bignum would have to be explicitly "cast" to a type object or
> converted to a string.  The service should decide what to do with it.
> > With the above-mentioned chaining, though, I can do
> >   /pgpinfo->methodCallChain('key', ['factor', 23940])
> > which will return the correct result.
> Why not just /pgpinfo->factor_key(23940)?
> >   This will also save a round-trip and possibly bignum-conversions.
> so does the above and it is a lot nicer

Yes, you can of course just design the DBus-exposed API for special cases, 
but this misses the point.
  I want to use the API (i.e. the class definitions) that are *already* 
available through the language, and to do this efficiently.

And yes of course the syntax I gave is very ugly - it could be seriously 
cleaned up, depending on the language (e.g. as a first approximation the
pgpinfo.chain(2).key.factor(23940) example I gave).  See also the bottom 
of this message..

> >   I see much traffic on the DBus list regarding C bindings like GLib.  
> > The content of this posting may not seem as relevant if you are calling 
> > *out* to C.  But, if you are trying to interface languages where 
> > "Everything is an Object" (e.g. Smalltalk), I think some solution of this 
> > nature will be important.
> > 
> Sorry to be over critical of this idea but it does look like solution in
> search of a problem.

Criticism is welcome :).  I am definitely partial to elegant solutions, 
not bloated ones.

A real example application: 
  I now have some bindings working where Python and Smalltalk 
intercommunicate to do 3D rendering, using the native Smalltalk types and 
functions.  E.g. a render method called by the render: method of a Squeak 
TDBusProxy object:
    def render(self, ogl):
        #print("Python TObject: would render with ogl=%s!\n" % ogl)
        sqobj(ogl).glColor3f_with_with(0.5, 0.5, 0.5)
        sqobj(self.myobj).renderCube_scale(ogl, 1.0)

Here 'ogl' is a class representing an OpenGL interface drawing to a 
particular OpenGL context in the Squeak program (well, Croquet actually - 
see, and 'myobj' refers to the TDBusProxy object in the 
squeak program..

I'm not claiming this is the best way to do 3D rendering or anything - 
just showing what I want to be able to do, without defining interfaces on 
top of those already present.

(note this example doesn't actually use methods on simple types; the 
point is an interface without "surprises")

>  I think well thought out API's is the solution to
> the round trip problem as well as not using DBus for lowlevel
> operations.  Keeping the bindings simple and maintainable is also a huge
> goal that this would complicate.  Really DBus is not "the" technology
> for lack of a better phase.  It is an enabler that enables other
> technologies.  Adding something like this puts rules into DBus that I
> believe should be left to the author of the API being wrapped by DBus.

I don't necessarily disagree.  I'm just interested in discussing how to 
map such higher-level interfaces naturally with DBus as-it-is.
  A basic issue in such an interface is how to send messages to types that 
DBus considers basic.
  The (fairly unattractive, I'll admit) call-chaining I proposed is simply 
a solution to this problem that DOESN'T require changes to DBus or lots of 
layers around it (I did consider many other ways first).

I have never used Glib, so I'm sure I don't understand the point of view 
of people heavily tied into it.  But since DBus already has Python, Ruby, 
etc. bindings I'm guessing there will be some people interested in the 


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