The following code is somewhat experimental. I have seen quite a few variations on this theme.  However, I believe this code does things in a new and interesting way.  This code is not feature complete, it is primarily a proof of concept at this point.  Please feel free to make comments and/or criticize this code.  If you have feature/code suggestions please feel free to add them to this page.  If you would like to submit code changes, please email them to me and I will review them for addition.

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This code allows for the following concepts/constructs:

   * "classes" definitions or "what procs and variables do all instances of this class have?"
   * "objects" or "an instance of a class."
   * Now supports transparent usage of class variables and procs from inside the class.
   * "interfaces" or "what procs are required to implement this interface?"
   * "comment" blocks inside class and interface declarations.
   * "options" or "what optional features are enabled for this class or interface?"
   * "single inheritance" or "procs from this other class are now in this class."
   * "multiple inheritance" or "procs from these other classes are now in this class."
   * "nested inheritance" or "procs from the base of my base are now in this class."
   * "constructors" and "destructors", that can take parameters and can prevent the object from being created/destroyed.

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The only "missing" things that I can think of so far are:

   * Being able to delegate a method to one of your bases.
   * A nice way to handle "conflicts" between procs in the immediate class and the bases (perhaps in more than one base).  Currently, if a proc exists in the immediate class, it is always called.  The result of calling a non-qualified proc that exists in more than one base class is undefined.
   * The ability to control access to the procs of a class (public, private, etc).

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This code is now too big for a WiKi page (about 100K, including test files).  

It may be downloaded from: http://www.tclbridge.com/tcl_oo.zip

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Here's a simple example of how to declare and use a class with this OO system...

 class demoClass {
   option alias.primary
   option proc.trace.outer
   option proc.trace.inner

   variable x
   variable y
   variable z
   variable array_variable

   comment {
     #
     # override global proc locally...
     # (notice we call the global proc from inside it)
     #
   }
   proc class_output { output } { 
     ::class_output "$this: $output"; # calls global proc 
   }

   proc constructor { object args } { 
     class_output "NEW: $this"; return "1" 
   }

   proc destructor { object args } { 
     class_output "DELETE: $this"; return "1" 
   }

   proc doNothing {a} {}

   proc simpleReturn {} { return $x.$y }

   proc returnMethod {a} { return [doNothing $a] }

   proc callMethod {a} { $this doNothing $a; return $x }

   proc testArray {} {
     set array_variable(1) "element1"
     set array_variable(2) "element2"
     set array_variable(3) "element3"
     return [array names array_variable]
   }
 }

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Written By [Joe Mistachkin]

 Version History

   * 19/Nov/2002 Version 1.00 -- initial release.
   * 19/Nov/2002 Version 1.20 -- added transparent access to class variables.
   * -- streamlined some of the code.
   * -- more comprehensive cleanup of variables, procs, and namespaces.
   * 20/Nov/2002 Version 1.25 -- more robust handling of invalid class declarations.
   * -- added tests for arrays inside classes.
   * 20/Nov/2002 Version 1.30 -- more argument validation.
   * -- added more tests dealing with invalid class declarations.
   * -- added class_objects proc to return a list of active objects for a class.
   * 20/Nov/2002 Version 1.31 -- fixed error handling for a certain test case involving bad class declarations.
   * 20/Nov/2002 Version 1.32 -- fixed problem preventing multiple matches in class_objects.
   * 22/Nov/2002 Version 1.40 -- added support for interfaces.
   * -- added support for comment blocks inside classes and interfaces.
   * -- cleaned up and organized tests.
   * -- changed some error messages.
   * -- other miscellaneous changes.
   * 13/Mar/2003 Version 1.60 -- added support for inheritance, single and multiple.
   * -- a lot of cleanup and reorganization.
   * -- added support for implementing an interface using base classes.
   * -- added more introspection features.
   * -- added support for parameterized constructors/destructors (can stop creation/destruction).
   * 13/Mar/2003 Version 1.61 -- corrected loop invariant for interface definitions.
   * 15/Mar/2003 Version 1.75 -- massive internal changes to namespace handling.
   * -- added support for nested inheritance.
   * -- added first stages of "conflict resolution" (currently, there is none).
   * -- cleaned up class_hasProc.
   * -- massively changed and streamlined class_findProc.
   * -- added more introspection commands.
   * -- added more tests to "class_test2.tcl".
   * 16/Mar/2003 Version 1.89 -- more massive changes to namespace handling.
   * -- added support for class and interface "options".
   * -- removed some old dead code.
   * -- changed proc aliasing to be more robust, aliases are now visible within the namespace of the calling object only.
   * -- added support for a variable number of arguments to procs defined with an "args" parameter as the last parameter.

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[Category Object Orientation]