为什么不能C＃中使用内联匿名lambda表达式或代表？ [英] Why can't c# use inline anonymous lambdas or delegates?

问题描述

我希望我的措辞恰当，我的问题的称号。

I hope I worded the title of my question appropriately.

在C＃中我可以使用lambda表达式（作为代表），或上了年纪的委托语法来做到这一点：

In c# I can use lambdas (as delegates), or the older delegate syntax to do this:

Func<string> fnHello = () => "hello";
Console.WriteLine(fnHello());

Func<string> fnHello2 = delegate()
{
    return "hello 2";
};
Console.WriteLine(fnHello2());

那么，为什么我不能内联拉姆达或委托身体，避免捕捉它在一个名为变量（使其匿名）？

So why can't I "inline" the lambda or the delegate body, and avoid capturing it in a named variable (making it anonymous)?

// Inline anonymous lambda not allowed
Console.WriteLine(
    (() => "hello inline lambda")()
);

// Inline anonymous delegate not allowed
Console.WriteLine(
    (delegate() { return "hello inline delegate"; })()
);

这在JavaScript（只是比较）工作的一个例子是：

An example that works in javascript (just for comparison) is:

alert(
    (function(){ return "hello inline anonymous function from javascript"; })()
);

这产生预期的警告框。

Which produces the expected alert box.

更新：
看来你的可以的在C＃中联匿名的lambda，如果将适当的，但（）的开工量，使其不羁。

UPDATE: It seems you can have an inline anonymous lambda in C#, if you cast appropriately, but the amount of ()'s starts to make it unruly.

// Inline anonymous lambda with appropriate cast IS allowed
Console.WriteLine(
    ((Func<string>)(() => "hello inline anonymous lambda"))()
);

或许编译器不能推断匿名委托的SIG知道哪些Console.WriteLine（）你想打电话？有谁知道为什么需要这个特定的投？

Perhaps the compiler can't infer the sig of the anonymous delegate to know which Console.WriteLine() you're trying to call? Does anyone know why this specific cast is required?

推荐答案

lambda表达式在C＃中没有的类型，直到他们在他们强制转换为委托或防爆pression类型上下文中使用。这就是为什么你不能说

Lambdas in C# do not have types, until they are used in a context that casts them to a delegate or Expression type. That's why you can't say

var x = () => "some lambda";

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