Ariteit

Ariteit, known in English as arity, is the number of arguments that a function expects. In mathematics, a function f that takes n inputs and returns an output has arity n. In programming, arity describes the function's signature: a nullary function takes no arguments, unary takes one, binary two, and so on. Variadic functions accept a variable number of arguments, sometimes with a fixed base plus additional values. In Dutch contexts the term ariteit is commonly used, while arity is the broader English counterpart.

Fixed-arity definitions contrast with variadic forms. Some languages separate fixed-arity definitions from variadic ones, while others support features such as rest parameters, variadic generics, or templates to handle different arities. In languages that use currying, such as Haskell, a function that appears to take multiple arguments is often represented as a chain of single-argument functions; the practical arity can be seen as the length of that chain rather than a single call’s parameter count.

Ariteit influences programming practices in several ways. It affects how functions are composed, how partial application or currying is performed, and how APIs are designed. Many languages provide mechanisms to query arity at runtime or to enforce it at compile time. Examples include runtime properties like function.length in JavaScript or arity metadata in reflection, and compile-time checks in statically typed languages.

Understanding ariteit helps in reasoning about function interfaces, higher-order functions, and the limits of partial application and function composition.