Timeline for Argument contravariance, real world purpose and usage?

6 events

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Jan 30, 2018 at 15:38	comment	added	Erik Eidt		There is another example in that article: The `Circle` class inherits `Shape` and overrides `Area`. The example creates a `SortedSet<T>` of `Circle` objects, using a constructor that takes an `IComparer<Circle>`. However, instead of passing an `IComparer<Circle>`, the example passes a `ShapeAreaComparer` object, which implements `IComparer<Shape>`. The example can pass a comparer of a less derived type (`Shape`) when the code calls for a comparer of a more derived type (`Circle`), because the type parameter of the `IComparer<T>` generic interface is contravariant.
Jan 30, 2018 at 14:57	history	edited	Joel Harkes	CC BY-SA 3.0	added 281 characters in body
Jan 30, 2018 at 14:55	history	edited	Deduplicator	CC BY-SA 3.0	added 25 characters in body
Jan 30, 2018 at 14:54	comment	added	Joel Harkes		if `CatShelter` implementation would also be able to store Objects. (this class is also used directly, not through interface) then you don't need another method to implement the interface.
Jan 30, 2018 at 14:49	comment	added	John V		I can see even WIkipedia describes that with the CatShelter example, which in derived class accepts the Animal type (en.wikipedia.org/wiki/…). But I just cannot see jhow this is useful and why
Jan 30, 2018 at 14:32	history	answered	Joel Harkes	CC BY-SA 3.0