不是C＃的接口，为什么可以包含字段？ [英] Why can't C# interfaces contain fields?

问题描述

例如，假设我想要一个 ICAR 接口，并且所有的实现将包含字段年度。这是否意味着每一个实现必须单独声明年度？那岂不是更好只需在接口定义这个？

For example, suppose I want an ICar interface and that all implementations will contain the field Year. Does this mean that every implementation has to separately declare Year? Wouldn't it be nicer to simply define this in the interface?

推荐答案

虽然很多其他的答案都在语义层面正确的，我觉得很有意思也接近这些各种各样的从实现细节层次的问题。

Though many of the other answers are correct at the semantic level, I find it interesting to also approach these sorts of questions from the implementation details level.

一个接口可以被认为是的插槽的，其中包含的方法的集合。当一个类实现一个接口，这个类必须告诉运行时如何在所有需要的插槽填写。当你说

An interface can be thought of as a collection of slots, which contain methods. When a class implements an interface, the class is required to tell the runtime how to fill in all the required slots. When you say

interface IFoo { void M(); } 
class Foo : IFoo { public void M() { ... } }

类说当你创建了我的一个实例，工具和IFoo.M.在插槽Foo.M参考

the class says "when you create an instance of me, stuff a reference to Foo.M in the slot for IFoo.M.

然后，当你做一个电话：

Then when you do a call:

IFoo ifoo = new Foo();
ifoo.M();

编译器生成code，上面写着问对象什么方法是在IFoo.M插槽，并调用该方法。

the compiler generates code that says "ask the object what method is in the slot for IFoo.M, and call that method.

如果一个接口是包含方法，插槽的集合，然后其中的一些槽也可以包含一个属性，则get的get和set方法和索引器的设置方法，以及添加和删除事件的方法。但字段是不是方法。有一个领域，你就可以填充与外地位置的引用相关联的槽。因此，接口可以定义方法，属性，索引和事件，但并非领域。

If an interface is a collection of slots that contain methods, then some of those slots can also contain the get and set methods of a property, the get and set methods of an indexer, and the add and remove methods of an event. But a field is not a method. There's no "slot" associated with a field that you can then "fill in" with a reference to the field location. And therefore, interfaces can define methods, properties, indexers and events, but not fields.

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