Arityzero

Arityzero, or arity-0, refers to a function, operation, or construct that accepts no input arguments. In formal terms, its arity is zero. In many languages and frameworks, a zero-arity element is called nullary.

In programming, a nullary function is a function that can be invoked without any parameters to yield a value. Some languages support true zero-argument functions, whereas others model such behavior as constants or as functions of a unit type due to currying. For example, in Python, def f(): return 42; f() is a zero-argument function. In JavaScript, const f = () => 42; f() is likewise zero-arity. In purely curried languages such as Haskell, what looks like a zero-argument value is often represented by a function awaiting a unit or by a value bound in a closure.

Nullary constructs are common for constants, configuration getters, or parameterless initializers. In APIs and interfaces, arity-zero endpoints or procedures are those that require no input parameters, returning a result or performing a side effect.

See also arity, nullary, unary, binary, unit type, currying.

Arityzero is a descriptive label used in informal discussion of zero-argument programming constructs. It is not a formal specification in all communities, where terms like nullary or arity-0 are preferred.