On Feb 7, 2005, at 10:20 PM, Gustaf Neumann wrote:

did you try this example out of curiosity or do you have an interesting example?

Mostly out of curiosity. I was also wondering if you could do a prototype object system in XOTcl (where one can inherit from any object) so then I started to wonder if it would possible in XOTcl to promote any object to a class.

-gustaf PS: i did not know that you are using a Mac...

Yup. Got myself a Powerbook a couple of months ago and am very pleased with it (after the problems with a Linux laptop it has been very refreshing). Great AquaTclTk package for it too which includes XOTcl.

/ http://www.fishpool.com/~setok/

...

There are two fixes for that, one simple (don't allow reclassing of objects to classes) or a more complex one (do more or less a recreate automatically when this happens; it tries to keep the object information as far as possible).

I don't know the internals really of XOTcl but basically making an object a class would mean giving it the methods 'instproc' and 'new' and various other stuff, thus allowing an instance of it to be created. I guess it's some internal thing if it has to be recreated? In some sense it would be 'pure' if this was possible.

From the C level, a class has to keep more information than an object. The class structure is an extension of an object, containing hash tables and a couple of pointers:

typedef struct XOTclClass { struct XOTclObject object; struct XOTclClasses* super; struct XOTclClasses* sub; short color; struct XOTclClasses* order; struct XOTclClass* parent; Tcl_HashTable instances; Tcl_Namespace *nsPtr; Tcl_Obj* parameters; XOTclClassOpt* opt; Tcl_HashTable *nonposArgsTable; } XOTclClass;

therefore classes need somewhat more memory than objects, these structures have to be allocated and maintained, so everything is a little more costly than it has to for objects.

Providing means to make "obj class Class" and "cl class Object" working is certainly doable, but i am not sure that is worth the effort, since one can achieve similar effects already from the tcl level (see below).

I wonder if this has any relevance to changing the meta-class of a class?

Check out the code below, it might be pretty close to what you might be thinking about.

-gustaf =============================================================== package req XOTcl namespace import ::xotcl::*

# we will defined our own Class and Object commands namespace forget Class Object

# redefine Class and Object ::xotcl::Class create Class -superclass ::xotcl::Class Class instproc unknown {m args} {puts "[self] unknown called for $m $args"} Class instproc init {} { set sc [my info superclass] if {$sc eq "::xotcl::Object"} {set sc [list]} my superclass [concat $sc Class] } ::xotcl::Class Object -superclass Class

# create some object Object c

# ... which is a class that can create an object ... c create d # ... and so on ... d create e

# provide a method d instproc foo {} {puts [self proc]}

# call the method from it's instance e foo

# create another object which should use the methods provided # by some other objects.... e create f -mixin d

# call the method f foo