C# 10 Pocket Reference by Joseph Albahari & Ben Albahari

Author:Joseph Albahari & Ben Albahari [Joseph Albahari]
Language: eng
Format: epub
Publisher: O'Reilly Media, Inc.
Published: 2022-01-24T16:00:00+00:00

public interface IPushable<in T> { void Push (T obj); }

we can legally do this:

IPushable<Animal> animals = new Stack<Animal>(); IPushable<Bear> bears = animals; // Legal bears.Push (new Bear());

Mirroring covariance, the compiler will report an error if you try to use a contravariant type parameter in an output position (e.g., as a return value, or in a readable property).

Delegates

A delegate wires up a method caller to its target method at runtime. There are two aspects to a delegate: type and instance. A delegate type defines a protocol to which the caller and target will conform, comprising a list of parameter types and a return type. A delegate instance is an object that refers to one (or more) target methods conforming to that protocol.

A delegate instance literally acts as a delegate for the caller: the caller invokes the delegate, and then the delegate calls the target method. This indirection decouples the caller from the target method.

A delegate type declaration is preceded by the keyword delegate, but otherwise it resembles an (abstract) method declaration. For example:

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