.net 为什么某些 C# lambda 表达式编译为静态方法

发布于09月01日

正如您在下面的代码中所看到的，我已将Action<>对象声明为变量.

有人能告诉我为什么这个动作方法委托的行为像一个静态方法吗？

为什么在下面的代码中返回true？

代码:

public static void Main(string[] args)
{
    Action<string> actionMethod = s => { Console.WriteLine("My Name is " + s); };

    Console.WriteLine(actionMethod.Method.IsStatic);

    Console.Read();
}

输出:

示例输出样本

推荐答案

这很可能是因为没有闭包，例如:

int age = 25;
Action<string> withClosure = s => Console.WriteLine("My name is {0} and I am {1} years old", s, age);
Action<string> withoutClosure = s => Console.WriteLine("My name is {0}", s);
Console.WriteLine(withClosure.Method.IsStatic);
Console.WriteLine(withoutClosure.Method.IsStatic);

这将为withClosure输出false，为withoutClosure输出true.

当您使用lambda表达式时，编译器会创建一个小类来包含您的方法，这将编译成如下所示(实际实现很可能略有不同):

private class <Main>b__0
{
    public int age;
    public void withClosure(string s)
    {
        Console.WriteLine("My name is {0} and I am {1} years old", s, age)
    }
}

private static class <Main>b__1
{
    public static void withoutClosure(string s)
    {
        Console.WriteLine("My name is {0}", s)
    }
}

public static void Main()
{
    var b__0 = new <Main>b__0();
    b__0.age = 25;
    Action<string> withClosure = b__0.withClosure;
    Action<string> withoutClosure = <Main>b__1.withoutClosure;
    Console.WriteLine(withClosure.Method.IsStatic);
    Console.WriteLine(withoutClosure.Method.IsStatic);
}

您可以看到生成的Action<string>个实例实际上指向这些生成的类上的方法.