C#3.5委托语法(Lambda表达式) [英] C# 3.5 Delegate Syntax (Lambda Expression)

问题描述

订阅我的委托方法时，我只是对奇怪的问题感到困惑:

在以下情况下可以正常工作:

Hi,

I am just confused around strange issue when subscribing my method to delegate:

Work ok on below scenarion:

Public void Test()
{

//Func<int,> objFunc = null;  ---------Line 1
//objFunc += (x) => { return x == 5; };--------Line 2

//Func<int,bool> objFunc += (x) =>{ return x == 5; };---------Line 3

}

在上面的代码片段中，如果我注释第3行，则它将编译.但是，如果我注释第1行，第2行和取消注释第3行，则不会编译.

有什么问题?难道这两个东西都一样吗?

请在这方面帮助我.

谢谢!!!

[添加了代码块以提高可读性]

In above code snippet, If I comment Line 3, then it compiles will. But if i comment Line 1 , Line 2 and Uncomment Line 3, it does not compiles.

What is the issue? arent both the things same ?

please help me on this regard.

Thanks!!!

[added code block for better readability]

推荐答案

没有这样的东西订阅我的方法来委托".

您创建一个委托实例，并将匿名方法添加到其调用列表中.

There is no such thing "subscribing my method to delegate".

You create a delegate instance and add an anonymous method to its invocation list.

System.Action<int, string> myAction = null;
myAction += (number, format) => {
    System.Console.WriteLine(format, number); //for example
};

System.Action<int, string>是委托类型，myAction是委托实例.
您应该理解，在调用列表中添加另一种方法会更改变量的引用标识.

Here System.Action<int, string> is a delegate type, myAction is a delegate instance.
You should understand, that adding one more method to the invocation list change referential identity of the variable.

System.Action<int, string> myAction = null;
myAction += (number, format) => {
    System.Console.WriteLine(format, number); //for example
};
System.Action<int, string> oldAction == myAction;
myAction += (number, format) => { /*...*/ };

//at this moment, oldAction != myAction; object.ReferenceEquals(oldAction, myAction) == false;

因此，当您执行此操作(+=)时，将创建一个全新的委托实例并将其分配给变量.换句话说:委托实例是不可变的.为什么?出于与字符串相同的原因:线程安全.

有什么问题吗?

—SA

So, when you do this operation (+=), a brand new delegate instance is created and assigned to a variable. In other words: delegate instances are not mutable. Why? For the same reason as strings: thread safety.

Any questions?

—SA

第1行的语法错误.这就是第1行和第2行出错的原因.应该是

Line 1 has the wrong syntax. That is why Lines 1 and 2 are erroring out. It should be

Func<int,bool> objFunc = null;

我认为这里的问题是，在告诉编译器objFUnc是什么之前，您试图为其分配功能..

line1，lin2确保一旦声明了委托，然后为其分配了功能，就可以添加许多类似于line2的功能...

I think the problem here us that before telling the comiler what objFUnc is , u r trying to assign functinality to it..

line1,lin2 makes sure that once delegate is declared and then functionality is assigned to it , many functionalitites similar to line2 can be added...

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