Re: [Xotcl] [self class] inside [eval]

From: Gustaf Neumann <neumann_at_wu-wien.ac.at>
Date: Tue, 14 Sep 2004 14:12:59 +0200

Dear all,
i just returned from vacation and i am slowly digging through my mail.

> That's fine, just so I know that's not the intended use. Though I still
> think it may be interesting to have a method that would allow access to
> methods and everything in that fashion, but that may not be feasible.

the method eval is defined in predefined.xotcl through instforward.

# provide some Tcl-commands as methods for Objects
foreach cmd {array append lappend trace eval} {
  ::xotcl::Object instforward $cmd -objscope
}

the option -objscope means, that the instvars of the object
are in the current scope of evaluation and can be reached
without any prefix. one can do

~/scripts> Object o
::o
~/scripts> o set x 1
1
~/scripts> o incr x
2
~/scripts> o eval regexp b abc y
1
~/scripts> o info vars
x y
~/scripts> o set y
b

See the documentation of 1.3 for more details about
the forwarding stuff

accessing methods in general only through the namspace
is not possible, since we have procs+instprocs (of several
classes) with the same name. you certainly can call
a proc of the object via the eval method

~/scripts> o proc x {} {puts hu}
~/scripts> o eval x
hu

but not instprocs. The following explanation is only for advanced
readers:
<techyspeak>
  in XOTcl, instprocs are defined as Tcl-procs within class-specific
  namespaces. Therefore we can have a method with the same
  name in various classes, which are linked via the next-path.

  the class specific namespace for the methods of ::xotcl::Object
  is ::xotcl::classes::xotcl::Object. you can see the instprocs of
  ::xotcl::Object via:

     ~/scripts>info procs ::xotcl::classes::xotcl::Object::*

  If one defines a method in a class
     ~/scripts> Object instproc y {} {puts ho-[self]}
  it shows up there as well
    ~/scripts> info procs ::xotcl::classes::xotcl::Object::y
    ::xotcl::classes::xotcl::Object::y

  if for some reason, one has to call the instproc directly,
  one could use the forwarder

     ~/scripts> Object instproc y {} {puts ho-[self]}
     ~/scripts> o eval y
     ho-::o
 
 or e.g. the approach in "Itcl in XOTcl" http://mini.net/tcl/10975
 where itcl methods are called just by their names
 (i have somewhere a slightly faster version using "interp alias").
</techyspeak>

I would not recommend this for the general usage, since
- as uwe pointed out - this is bypassing the xotcl dispatcher
an can lead to unexpected behavior (it is a defined behavior,
but different from the variant without eval).

hope, this helps,
-gustaf

-- 
Univ.Prof. Dr.Gustaf Neumann
Abteilung für Wirtschaftsinformatik und Neue Medien
Wirtschaftsuniversität Wien, Augasse 2-6, 1090 Wien