C＃中通用Lazy类的协变使用 [英] Covariant use of generic Lazy class in C#

问题描述

假定适用：

public class Cat : Animal { }

并假设我有一个方法：

public void Feed(Animal animal) { ... }

我可以这样称呼：

var animal = new Cat();
Feed(animal);

当 Feed 时如何使此工作正常重构为仅支持 Lazy< Animal> 作为参数？我想以某种方式传递我的 var lazyAnimal = new Lazy< Cat>（）; 。

How can I get this working when Feed is refactored to only support Lazy<Animal> as parameter? I'd like to pass in my var lazyAnimal = new Lazy<Cat>(); somehow.

这显然不起作用：

var lazyAnimal = new Lazy<Cat>();
Feed(lazyAnimal);

推荐答案

好吧，您将无法使用它完全是这样。可能最简单的重构是让它接受 Func< Animal> 而不是 Lazy 。然后，您可以传入一个lambda来获取 Lazy 的值。 Func 就其返回类型而言是协变的。

Well, you won't be able to use it exactly as is. Probably the simplest refactor would be to have it accept a Func<Animal> instead of a Lazy. Then you could pass in a lambda that fetches the value of a Lazy. Func is covariant with respect to it's return type.

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