Nullary constructor


In computer programming, a nullary constructor is a constructor that takes no arguments. Also known as a 0-argument constructor or no-argument constructors.

Object-oriented constructors

In object-oriented programming, a constructor is code that is run when an object is created. Default constructors of objects are usually nullary.

Java example


public class Example

Algebraic data types

In algebraic data types, a constructor is one of many tags that wrap data. If a constructor does not take any data arguments, it is nullary.

Haskell example


-- nullary type constructor with two nullary data constructors
data Bool = False
| True
-- non-nullary type constructor with one non-nullary data constructor
data Point a = Point a a
-- non-nullary type constructor with...
data Maybe a = Nothing --...nullary data constructor
| Just a --...unary data constructor