Revision as of 20:02, 28 March 2025 edit Chriswjohnson (talk \| contribs) 23 edits Reworded the second paragraph, because the first sentence's structure, built around "how … relates to …", breaks its definition into separated halves, and readers must infer (due to the vagueness of "how") what type of thing "variance" might be. The next two sentences, both rhetorical questions, are converted to a single sentence of statements. NOTE: This edit would be significantly improved by enumerating variance types in sentence 1, and stating their effects on the examples in sentence 2. ← Previous edit		Revision as of 20:04, 27 May 2025 edit undo 90.189.205.194 (talk) Bivariance means equality of types. Tags: Reverted Visual edit Mobile edit Mobile web edit Next edit →
Line 109: == Inheritance in object-oriented languages == When a subclass [[Method overriding\|overrides]] a method in a superclass, the compiler must check that the overriding method has the right type. While some languages require that the type exactly matches the type in the superclass (~~invariance~~bivariance), it is also type safe to allow the overriding method to have a "better" type. By the usual subtyping rule for function types, this means that the overriding method should return a more specific type (return type covariance) and accept a more general argument (parameter type contravariance). In [[Unified Modeling Language\|UML]] notation, the possibilities are as follows (where Class B is the subclass that extends Class A which is the superclass): <gallery perrow="5" heights="190" caption="Variance and method overriding: overview">

Covariance and contravariance (computer science): Difference between revisions