C＃：创建类的实例化一个什么都不做动作 [英] C#: create a do-nothing Action on class instantiation

问题描述

我有一个类，用户可以通过一个操作进（或没有）

I have a class that the user can pass an Action into (or not).

public class FooClass<T> : BaseClass<T>
{
    public FooClass()
        : this((o) => ()) //This doesn't work...
    {
    }

    public FooClass(Action<T> myAction)
        : base(myAction)
    {
    }
}

---

基本上，我不能为null传递到了动作。但是，在同一时间，我不想强​​迫我的用户在动作通过。相反，我希望能够以动态创建一个什么也不做的行动。

---

Basically, I can't pass null into my base class for the Action. But, at the same time I don't want to force my user to pass in an Action. Instead, I want to be able to create a "do-nothing" action on the fly.

推荐答案

您想说

this(t => { })

认为它这样。您需要 T =>匿名表达体。在这种情况下，匿名表达体是表达式或块。你不能有一个空的表现，所以你不能表明空的方法体与表达式。因此，你必须使用一个块在这种情况下，你可以说 {} 来表示一个块有一个空的语句列表，因此是空的身体。

Think of it like this. You need t => anonymous-expression-body. In this case, anonymous-expression-body is an expression or a block. You can't have an empty expression so you can't indicate an empty method body with an expression. Therefore, you have to use a block in which case you can say { } to indicate the a block has an empty statement-list and is therefore the empty body.

有关详细信息，请参阅语法规范，附录b中。

For details, see the grammar specification, appendix B.

和这里的另一种方式来想起来，这是，你可以用它来发现这个对自己的一种方式。一个动作< T> 是发生在一个方法 T 并返回无效。您可以定义一个动作< T>通过非匿名方式或通过匿名方式。您正在试图找出如何使用匿名方式（或者更确切地说，一个非常特殊的匿名方法，即lambda表达式）做到这一点。如果你想通过一个非匿名的方法来做到这一点，你会说

And here's another way to think of it, which is a way that you could use to discover this for yourself. An Action<T> is a method that takes in a T and returns void. You can define an Action<T> via an non-anonymous method or via an anonymous method. You are trying to figure out how to do it using an anonymous method (or rather, a very special anonymous method, namely a lambda expression). If you wanted to do this via a non-anonymous method you would say

private void MyAction<T>(T t) { }

，然后你可以说

this(MyAction)

它采用的方法组的概念。但是现在你想将这个转换为一个lambda表达式。所以，我们只是采取的方法体，并使其成为lambda表达式。因此，我们扔掉私人无效MyAction< T>（T T）并将其替换为 T => 复制逐字方法体 {} 。

which uses the concept of a method group. But now you want to translate this to a lambda expression. So, let's just take that method body and make it a lambda expression. Therefore, we throw away the private void MyAction<T>(T t) and replace it with t => and copy verbatim the method body { }.

this(t => { })

景气

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