Covariance and contravariance (computer science): Difference between revisions

Revision as of 02:45, 28 May 2025

Revision as of 02:52, 28 May 2025

Line 19:

* ''covariant'' if it preserves the [[subtyping|ordering of types (≤)]], which orders types from more specific to more generic: If <code>A ≤ B</code>, then <code>I<nowiki><A> ≤ I<B></nowiki></code>;

* ''contravariant'' if it reverses this ordering: If <code>A ≤ B</code>, then <code>I<nowiki><B> ≤ I<A></nowiki></code>;

* ''bivariant'' if both of these apply (i.e., if <code>A ≤ B</code>, then <code>I<nowiki><A> ≡ I<B></nowiki></code>);<ref>{{notetag|1=This only happens in a pathological case. For example, <code>I<T> = int</code>: any type can be put in for <code>T</code> and the result is still <code>int</code>.</ref>}}

* ''variant'' if covariant, contravariant or bivariant;

* ''invariant'' or ''nonvariant'' if not variant.

Line 497:

* [[Inheritance (object-oriented programming)]]

* [[Liskov substitution principle]]

== Notes ==

{{notefoot}}

== References ==