Nullary constructor

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.

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 MyInteger {  private int data;  // Nullary constructor  public MyInteger() {  this(0);  }  // Non-nullary constructor  public MyInteger(int value) {  this.data = value;  }  int getData() {  return data;  }  void setData(int value) {  data = value;  } } 

C++ example

class Integer { private:  int data; public:  // Default constructor with parameters  // Leaving parameters unspecified defaults to the default value  Integer(int value = 0):  data{value} {}  [[nodiscard]]  int getData() const noexcept {  return data;  }  void setData(int value) noexcept {  data = value;  } } 

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 

See also

• Default constructor