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Practical Programming in Tcl & Tk, Third Edition
By Brent B. Welch

Table of Contents
Chapter 14.  Namespaces

[incr Tcl] Object System

The Tcl namespace facility does not provide classes and inheritance. It just provides new scopes and a way to hide procedures and variables inside a scope. There are Tcl C APIs that support hooks in variable name and command lookup for object systems so that they can implement classes and inheritance. By exploiting these interfaces, various object systems can be added to Tcl as shared libraries.

The Tcl namespace facility was proposed by Michael McLennan based on his experiences with [incr Tcl], which is the most widely used object-oriented extension for Tcl. [incr Tcl] provides classes, inheritance, and protected variables and commands. If you are familiar with C++, [incr Tcl] should feel similar. A complete treatment of [incr Tcl] is not made in this book. Tcl/Tk Tools (Mark Harrison, O'Reilly & Associates, Inc., 1997) is an excellent source of information. You can find a version of [incr Tcl] on the CD-ROM. The [incr Tcl] home page is:


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