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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

public class Example { protected int data; /* Nullary constructor */ public Example() { this(0); } /* Non-nullary constructor */ public Example(final int data) { this.data = data; } }

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

References

1. "Default Constructor in Java – Class Constructor Example". freeCodeCamp.org. 2022-01-13. Retrieved 2022-03-23. https://www.freecodecamp.org/news/default-constructor-in-java/ ↩

2. "No-argument Constructor". chortle.ccsu.edu. Retrieved 2022-03-23. https://chortle.ccsu.edu/java5/Notes/chap50/ch50_13.html ↩

3. "Default constructors - cppreference.com". en.cppreference.com. Retrieved 2023-04-12. https://en.cppreference.com/w/cpp/language/default_constructor ↩

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 2022-03-23 978-1-4842-7337-1 ↩