OTcl

OTcl, short for Object Tcl, is an object-oriented extension to the Tcl scripting language. It provides a class- and object-based programming model for Tcl applications, enabling encapsulation, inheritance, and polymorphism within the Tcl environment. OTcl was developed to bring familiar OO concepts to Tcl without switching to a different language.

Historically, OTcl appeared in the late 1990s as one of several attempts to add OO support to Tcl before the introduction of TclOO in later Tcl versions. It was used in various Tcl/Tk projects to organize large codebases and to reuse components through inheritance and object composition. OTcl extensions were distributed as libraries that users loaded into their Tcl interpreters.

Core concepts include classes that define a set of methods and instance variables, objects created from those classes, and message passing to invoke methods. The system supports inheritance between classes, method overriding, and dynamic creation of new behavior at runtime. OTcl aimed to be lightweight and integrate closely with Tcl syntax, allowing objects to be used alongside plain Tcl commands.

OTcl can be compiled or linked as an extension and interfaced with C or C++ code for performance-critical components. It typically provides mechanisms for introspection, enabling programs to query class hierarchies and object attributes.

With the introduction of TclOO as part of core Tcl in later versions, OTcl gradually became less central. Some projects still use OTcl due to legacy code or specific OO semantics. Today, it is considered a historical approach to OO in Tcl, with TclOO serving as the standard object system in modern Tcl.