QTtype

QTtype is an open specification and accompanying tooling for describing and enforcing type information within the Qt software ecosystem. It provides a language for declaring data types, their constraints, and their serialization behavior, with the goal of improving interoperability between C++ backends and QML front ends, as well as across processes that communicate via Qt's data formats.

The QTtype language defines primitive types (such as Int, UInt, Float, Bool, String, DateTime) and composite types (List<T>, Map<K,V>, Optional<T>, Tuple). It supports user-defined types built from records and enums, as well as generic type aliases and modules. Constraints can express ranges, patterns, and validity rules, and there are facilities for versioned schemas and backward compatibility. The type system is designed to map cleanly to Qt's meta-object system and QVariant compatibility.

Tooling includes a validator and code generator. The validator checks QTtype definitions for consistency and compatibility with existing Qt code, while the code generator can emit C++ headers, QML type registrations, or bindings for other languages that interoperate with Qt data.

In practice, QTtype is used to define API contracts, data models for IPC, and data interchange formats such as network messages or local storage schemas. It aims to reduce runtime errors by catching type mismatches at build time and providing clear, machine-readable documentation.

QTtype originated as an open-source project to formalize type usage in Qt projects and is maintained by a community consortium. It remains experimental in some environments and has seen adoption in projects that require strict API contracts and automatic binding generation.