Gtype

GType is the core type system used by the GLib library, and by extension the GObject object framework, to implement dynamic typing and object-oriented programming in C. It provides a runtime registry of types, enabling a program to discover, inspect, and interact with objects and values in a type-safe way despite C’s lack of native reflection.

The GType system assigns a unique numeric identifier to every registered type. Types can be fundamental (such as basic string or object types) or derived from other types, forming a hierarchy that supports runtime type checking and safe casting. Information about each type—its name, size, parent type, and associated class structure—is stored in the type database and can be queried through the API. This enables features commonly associated with dynamic languages, such as runtime introspection, interfaces, and signals, within the GLib/GObject ecosystem.

Types are registered using static or dynamic registration functions, and the system is designed to support both static class definitions and dynamic type creation. Modern GLib code typically uses macros and helper functions (for example, macros to declare a new type and functions to define its initialization and finalization) to integrate with GType, GObject, and the object chemistry of GTK and related projects.

Common usage within GLib-based applications includes creating new GObject subclasses, leveraging type checking and casting, and enabling property and signal systems that rely on registered types. The GType system underpins much of the object-oriented programming style available in GNOME-era libraries, balancing C’s performance with a structured, introspective type model.

See also GLib, GObject, GTK.