设置无类型静态方法在泛型类 [英] Set no type for a static method in a generic class

问题描述

不是Java的粉丝，但Java允许不是一般类，并在这种情况下，它的威胁类型对象设置类型键入。不过，据我所知，C＃强制设定<的类型; T>随时泛型类已被实例化或简单来说使用。然而，让我们说，我们有一个通用类，我们需要在那里一个静态方法，它不依赖于<的类型; T> 。

Not a fan of Java, but Java allows not setting types for generic classes and in that case it threats the type as Object type. However, as far as I know, C# enforces setting the type of <T> anytime the generic class has to be instantiated or simply speaking used. However, let's say that we have a generic class, and we need a static method in there which does not rely on the type of <T>.

首先，我们知道，它可以移动到一个单独的上下文，或者我们可以设置一个虚拟的类型<的; T> ，但作为一个编程的难题有没有办法来调用它的没有定义 T 的类型？

Firstly, we know that it can be moved to a separate context or we can set a dummy type of <T>, but as a programming puzzle is there any way to call it Without defining the type of T?

例如：

 class Test<T> where T: ITestable {
     ...
     public static void CreateTestFile(String fileName) {...}
 }
 Test.CreateTestFile("test.txt");

这是可以做到的Java，显然不能在C＃。但我只是想确认一下。

This can be done Java and apparently can't be in C#. But I just wanna make sure.

推荐答案

Java和C＃实现泛型是不同的：

Java and C# implement generics differently:

• Java使用的类型擦除的，这基本上意味着，在编译的时候，任何事情你把< T> 擦除并成为对象。 东西<富> 和东西<酒吧GT; 将在运行时相同的类型，以及西港岛线是有效等于东西<对象>

• Java uses type erasure, which basically means that at compile time, anything you put in <T> is erased and becomes Object. Something<Foo> and Something<Bar> will be the same type at runtime, and wil be effectively equal to Something<Object>.

C＃使用的运行时物化的，意义对于每次与不同的 T 使用类型，运行时完全生成一个新的类，通过使用开放式泛型版本作为模板（这意味着它也产生了底层的本地每一次 T 正如你所说的话）的代码。 东西<富> 和东西<酒吧方式> 是两个不相关的类型至于CLR而言

C# uses run-time reification, meaning that for each type you use with a distinct T, the runtime generates a new class altogether, by using the open generic version as a template (which means it also generates the underlying native code once per T as you call it). Something<Foo> and Something<Bar> are two unrelated types as far as the CLR is concerned.

希望你明白，为什么这种差异对你的情况很重要。忽略 T 在Java小事，但在C＃中不那么容易了。

Hopefully you understand why this difference is important to your scenario. Ignoring T is trivial in Java, but not so easy in C#.

如果您不需要 T 在你的代码，然后使用非泛型方法：

If you don't need T in your code, then use a non-generic method:

abstract class Test
{
    public static void CreateTestFile(String fileName) {...}
}

class Test<T> : Test
    where T : ITestable
{
     ...
}

下面，那最好不过了：）

Here, that's better :)

此外，请注意实例方法，你可以使用的协的和的逆变的接口松动在编译时为一个已知 T 的要求。例如，如果您使用的是协变的界面，你只需要知道 T 的基本类型。

Also, note that for instance methods, you can use covariant and contravariant interfaces to loosen the requirement for a known T at compile-time. For instance, if you use a covariant interface, you only need to know a base type of T.

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