Nullary constructor

In computer programming, a nullary constructor is a constructor that takes no arguments. ^[1] Also known as a 0-argument constructor, no-argument constructor, ^[2] parameterless constructor or default constructor. ^[3]

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. ^[4]

Java example

publicclassMyInteger{privateintdata;// Nullary constructorpublicMyInteger(){this(0);}// Non-nullary constructorpublicMyInteger(intvalue){this.data=value;}intgetData(){returndata;}voidsetData(intvalue){data=value;}}

C++ example

classInteger{private:intdata;public:// Default constructor with parameters// Leaving parameters unspecified defaults to the default valueInteger(intvalue=0):data{value}{}[[nodiscard]]intgetData()constnoexcept{returndata;}voidsetData(intvalue)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 constructorsdataBool=False|True-- non-nullary type constructor with one non-nullary data constructordataPointa=Pointaa-- non-nullary type constructor with...dataMaybea=Nothing-- ...nullary data constructor|Justa-- ...unary data constructor

See also

• Default constructor

References

1. "Default Constructor in Java – Class Constructor Example". freeCodeCamp.org. 2022-01-13. Retrieved 2022-03-23.
2. "No-argument Constructor". chortle.ccsu.edu. Retrieved 2022-03-23.
3. "Default constructors - cppreference.com". en.cppreference.com. Retrieved 2023-04-12.
4. Ottinger, Joseph B.; Linwood, Jeff; Minter, Dave (2022), Ottinger, Joseph B.; Linwood, Jeff; Minter, Dave (eds.), "An Introduction to Hibernate 6" , Beginning Hibernate 6: Java Persistence from Beginner to Pro, Berkeley, CA: Apress, pp. 1–25, doi:10.1007/978-1-4842-7337-1_1, ISBN   978-1-4842-7337-1 , retrieved 2022-03-23