特定类的通用约束，为什么? [英] Generic constraints to a specific class, why?

问题描述

我一直在阅读利用泛型约束的知识，发现泛型可以限制为 struct ， class ， new ， Class 和 Interface .前三个背后的原因非常明显.但是我真的不明白为什么和何时约束一个班级.即

I've been reading on leveraging generic constraints, I've found that generics can be constrained to struct, class, new, Class and Interface. The reasons behind the first three are pretty obvious. But I can't really understand why and when to constraint to a class. i.e

class Foo<T> where T : Bar 
class Foo<T> where T : IBar

这使我们可以限制Bar和它的孩子，分别限制IBar和实现者.我们不能只为类或接口编程吗?因为这基本上就是多态性的用途，并且Microsoft工程师绝不会愚蠢地实现无用的功能.

This allows us to constrain to Bar and it's children, and IBar and implementers respectively. Can't we just program to the class, or the interface ? Because that's basically what polymorphism is for, and Microsoft Engineers are far from dumb to implement a useless feature.

我想念什么?

更新:

我的问题已被标记为重复:为什么在C#中使用泛型约束

My question has been marked as duplicate for : Why use generic constraints in C#

我认为并非如此.

我彻底解决了这个问题，但并没有真正找到答案:它讨论了一般约束的使用，而在这里我问的是为什么我们要约束到一个类或一个接口上，为什么不仅仅局限于此呢?直接编程吗?

I went through this question thoroughly, and didn't really find the answer: It discussed the use of generic constraints in general, while here I'm asking about why do we constrain to a class or an interface, why not just program to it directly ?

推荐答案

也许这个简单的示例可能会有所帮助.

Perhaps this simple example might help.

如果我有这些课程:

public class ListOfCars<T> : List<T> where T : Car { }

public abstract class Car { }
public class Porsche : Car { }
public class Bmw : Car { }

...然后，如果我编写这段代码:

...and then if I write this code:

var porsches = new ListOfCars<Porsche>();

// OK
porsches.Add(new Porsche());

//Error - Can't add BMW's to Porsche List
porsches.Add(new Bmw());

您会看到我无法将BMW添加到保时捷列表中，但是如果我只是在基类基础上进行编程，那将是允许的.

You can see that I can't add a BMW to a Porsche list, but if I just programmed off of the base class it would be allowed.

这篇关于特定类的通用约束，为什么?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！