Typelocality

Typelocality is a term used in discussions of programming language design and software architecture to describe how localized type information is within a software system. It refers to the extent to which a type is confined to a particular module, package, or lexical scope rather than being globally visible across the program. High typelocality means that most types are defined and used within well-defined boundaries, with explicit exports or interfaces that restrict access to internal representations. Low typelocality corresponds to broader visibility, where types propagate through interfaces or type inference across modules.

In practice typelocality is achieved through module systems, access modifiers, and opaque or abstract data types. Designers separate a module’s implementation from its public interface, exposing only the necessary type names and constructors, while keeping internal representations private. This supports encapsulation, safer refactoring, and easier independent compilation, since clients depend only on the exported surface.

Typelocality interacts with type inference and polymorphism. Strong locality may require explicit type exports, while type systems with gradual or global inference may blur boundaries. The trade-offs include potential boilerplate and greater discipline in module design against the benefits of modularity, binary compatibility, and clearer abstractions.

In related terminology, typelocality is often discussed alongside encapsulation, interface design, and the module system of a language. While not a formal standard, it provides a useful lens for evaluating how a language or architecture manages type information across components.