In computer programming, a nullary constructor is a constructor that takes no arguments. Also known as a 0-argument constructor, no-argument constructor, parameterless constructor or default constructor.
In object-oriented programming, a constructor is code that is run when an object is created. Default constructors of objects are usually nullary.
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.