From: Isaac Gouy <igouy@...>
Date: 2005-12-28T04:07:54+09:00
Subject: Re: Diff of opinion on dynamic stuff

Bob Hutchison wrote:
> On Dec 23, 2005, at 12:47 AM, Isaac Gouy wrote:
>
> > Yes, the equivalent of "method_missing" has been used for many things
> > in Smalltalk.  Glorifying in how we can hack "doesNotUnderstand:"
> > avoids having to admit that there's been a problem with the language.
>
> The problem being: in Smalltalk the language there is no explicit way
> in the language to add a method to a class at runtime?

Adding a method to a class at runtime is trivial, simply send the
message "compile: aMethodSourceString" to the class.

Integer compile: 'plus: anInteger
^self + anInteger'


afaict Over the years Smalltalk has accumulated a bunch of really
clever programming techniques to work-around the lack of meta protocols
for controlling message passing.

afaict CLOS provides directly what Smalltalk can only accomplish
indirectly - so we should celebrate "doesNotUnderstand:" trickery as
clever programming rather than clever language design.

>
> Maybe so, but the Smalltalk *environment* allows the programmer to do
> exactly the same thing as the browser or debugger at runtime (though
> only on a class level). In some implementations, there is a method
> that changes an object's class, and that combined with the ability to
> create a new class at runtime... (well, this is hard to manage, and
> some implementations will, effectively, only redefine the parent
> class of an object). This excessive use/dependency on
> doesNotUnderstand is not necessary in Smalltalk.
>
> Isn't re-opening a class very similar to some of the better methods
> in the paper below? At the very least, the associated problems are
> similar :-)
>
> What are the Python folks doing as an alternative?
>
> >
> > "This comparison highlights that the most commonly used technique
> > based
> > on the specialization of the doesNotUnderstand: method is not the best
> > one. As a first explanation of this situation, one should note that
> > the
> > ability to directly execute a method has only lately been
> > introduced in
> > the interpreters (methods valueWithReceiver:arguments: on
> > CompiledMethod class in VisualWorks and
> > executeWithReceiver:andArguments: in IBM Smalltalk). Moreover, this
> > comparison shows that the techniques based on VM lookup method or
> > method wrappers should be considered by more programmers than it is
> > currently the case."
> >
> > "Evaluating Message Passing Control Techniques in Smalltalk"
> > http://www.iam.unibe.ch/~scg/Archive/Papers/
> > Duca99aMsgPassingControl.pdf
>
> ----
> Bob Hutchison          -- blogs at <http://www.recursive.ca/hutch/>
> Recursive Design Inc.  -- <http://www.recursive.ca/>
> Raconteur              -- <http://www.raconteur.info/>