TclOO

TclOO is the object-oriented extension for the Tcl programming language, providing a class-based object system that is integrated into modern Tcl distributions. It offers a lightweight, Tcl-friendly approach to defining classes, creating objects, and invoking methods, and is intended as a practical alternative to older Itcl-style OO within Tcl.

Core concepts in TclOO include classes, objects, methods, and constructors. A class defines a set of behaviors (methods) and a per-object state (attributes or fields), while an object is an instance of a class. Methods are called on objects and can access or modify the object’s state via a special reference to the current instance. Constructors initialize new objects, and many implementations also provide a destructor or finalization hook for cleanup.

Inheritance and composition are supported through single inheritance and mixins, enabling a class to reuse and extend behavior from one or more parent sources. Method resolution follows a defined order that respects overrides in subclasses while preserving access to parent implementations when needed.

Usage of TclOO typically involves defining a class with a dedicated class-creation facility and then instantiating objects from that class. The system works within Tcl’s namespaces and is designed to be interoperable with other Tcl packages and toolkits, such as Tk for graphical interfaces. TclOO is well-suited for modeling widgets, services, and configuration objects within Tcl applications, and it is part of the standard Tcl ecosystem in recent releases.

See also: incr Tcl (Itcl), Tcl, Tk, object-oriented programming concepts in Tcl.