Introduction

Supporting XOTcl 1 in XOTcl 2

In general, the XOTcl 2 environment supports multiple object systems concurrently. Effectively, every object system has different base classes for creating both, objects and classes. Therefore, the object systems can have different different interfaces and names of builtin methods. Currently, XOTcl 2 supports primarily XOTcl 1 and XOTcl 2 (XOTcl 1 provides about twice as many predefined builtin methods).

The support for multiple object systems can be used to load XOTcl 1 and XOTcl 2 scripts into the same interpreter. This makes migration from XOTcl 1 to XOTcl 2 easier. The XOTcl environment provides the predefined command ::xotcl::use to make switching between these objects systems convenient. The following example script shows a single script defining classes of XOTcl 1 and 2:

   package require XOTcl

   namespace eval mypackage {

      # Some definitions for XOTcl 1
      ::xotcl::use xotcl1

      Class C1
      C1 instproc foo {} {puts "hello world"}

      # Some definitions for XOTcl 2
      ::xotcl::use xotcl2

      Class create C2 {
         :method foo {} {puts "hello world"}
      }
   }

"Switching" effectively means the load some libraries if needed and to import either the XOTcl 1 or XOTcl 2 base classes as Object and Class into the current namespace. If the import is not wanted, just use package require to load the necessary pieces.

XOTcl 1 Idioms in XOTcl 2

Defining Objects and Classes

Defining Methods

Resolvers

Invoking Methods

Accessing Instance Variables from Method Bodies

Accessing Instance Variables of other Objects

Object Parameters

Method Parameters

Introspection

List methods defined by objects

List methods defined by classes

List class object specific methods

List callable methods

List object/class where some method is defined

List definition of scripted methods defined by classes

List definition of scripted object specific methods

For definition of class object specific methods, use modifier object as shown in examples above.

List filter or mixins

List definition of methods defined by aliases, setters or forwarders

List fully qualified name of method

List type of a method

List the scope of mixin classes

Check properties of object and classes

Predefined Methods

Dispatch, Aliases, etc.

Assertions

Method Protection

Incompatibilities

Namespace resolvers

The XOTcl 2 namespace resolvers are use as well when XOTcl 1 is used within XOTcl 2.

Stronger Checking

XOTcl 2 performs stronger checking than XOTcl 1. The requiredness of slots in XOTcl 1 was just a comment, while XOTcl 2 enforces it.

Different results

• [self next] returns
  instead of "proc" and "instproc" => "method"
  instead of "parametercmd" and "instparametercmd" => "setter"
  instead of "instforward" => "forward"
  instead of "instcmd" => "cmd".
  The modifier "object" is added when needed.
• [self filterreg] returns
  instead of "instforward" => "forward"
  The modifier "object" is added when needed.

Exit handlers

The exit hander interface changed from a method of ::xotcl::Object into procs in the ::xotcl namespace. XOTcl 2 provides now:

   ::xotcl::setExitHandler script
   ::xotcl::getExitHandler
   ::xotcl::unsetExitHandler