Typed

Typed refers to data, variables, expressions, or languages that use a type system to classify values and constrain operations. When something is typed, its type helps determine what can be done with it, how it can be stored, and how it interacts with other data. In programming, many languages are described as typed because they assign types to values, functions, and data structures.

Typing can be static or dynamic. Static typing checks type correctness at compile time, catching many errors before the program runs. Dynamic typing checks types at runtime, offering more flexibility but potentially delaying error detection. Some languages support gradual typing, allowing mixed usage of typed and untyped code. Type systems can be nominal, where compatibility depends on declared names, or structural, where compatibility depends on the shape or structure of data. Duck typing is a dynamic form of structural typing common in dynamic languages, focusing on behavior rather than explicit type relations.

Type systems provide benefits such as early error detection, clearer documentation through explicit types, and opportunities for optimization. They may support type inference, where the compiler deduces types automatically, and type annotations, which explicitly specify types. Generics and polymorphism enable reusable code that works across multiple types.

Commonly typed languages include statically typed ones such as Java, C#, and Rust, and dynamically typed ones such as Python and JavaScript. Type systems vary in strictness and features; for example, TypeScript adds static typing to JavaScript, while Kotlin and Swift balance safety with practicality.

History and design play central roles in typing. Typed programming languages emerged in the mid-20th century, with formal type systems developed in academia and gradually adopted into mainstream languages. Today, typing remains a core consideration in language design and in data modeling.

See also: type system; type checking; type inference; static typing; dynamic typing.