System.Action的使用（lambda 表达式）

对于Action的使用方法使用如下：

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            string first = "First";
            var action = new Action(() => { Console.WriteLine(first); });
            action();

            var action2 = new Action<string>((s) => { Console.WriteLine($"Action<T>:{s}"); });
            action2(first);

            var action3 = new Action<string, string>((s1, s2) => {
                Console.WriteLine($"Action<T1,T2>:{s1},{s2}");
            });
            action3(first, "second");
        }
    }
}

使用dotPeek通过反编译，得到代码：

namespace ConsoleApp1
{
  internal class Program
  {
    private static void Main(string[] args)
    {
      string first = "First";
      ((Action) (() => Console.WriteLine(first)))();
      ((Action<string>) (s => Console.WriteLine(string.Format("Action<T>:{0}", (object) s))))(first);
      ((Action<string, string>) ((s1, s2) => Console.WriteLine(string.Format("Action<T1,T2>:{0},{1}", (object) s1, (object) s2))))(first, "second");
    }
  }
}

下面写一种与反编译出来的相似的方法

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            string first = "First";
            var action = new Action(() => { Console.WriteLine(first); });
            action();

            var action2 = new Action<string>((s) => { Console.WriteLine($"Action<T>:{s}"); });
            action2(first);

            var action3 = new Action<string, string>((s1, s2) =>
            {
                Console.WriteLine($"Action<T1,T2>:{s1},{s2}");
            });
            action3(first, "second");

            new Action(() => { Console.WriteLine(first); })();
            new Action<string>((s) => { Console.WriteLine($"Action<T>:{s}"); })(first);
            new Action<string, string>((s1, s2) =>
            {
                Console.WriteLine($"Action<T1,T2>:{s1},{s2}");
            })(first, "second");
        }
    }
}

看一下反编译的结果：

namespace ConsoleApp1
{
  internal class Program
  {
    private static void Main(string[] args)
    {
      string first = "First";
      ((Action) (() => Console.WriteLine(first)))();
      ((Action<string>) (s => Console.WriteLine(string.Format("Action<T>:{0}", (object) s))))(first);
      ((Action<string, string>) ((s1, s2) => Console.WriteLine(string.Format("Action<T1,T2>:{0},{1}", (object) s1, (object) s2))))(first, "second");
      ((Action) (() => Console.WriteLine(first)))();
      string str1 = first;
      ((Action<string>) (s => Console.WriteLine(string.Format("Action<T>:{0}", (object) s))))(str1);
      string str2 = first;
      string str3 = "second";
      ((Action<string, string>) ((s1, s2) => Console.WriteLine(string.Format("Action<T1,T2>:{0},{1}", (object) s1, (object) s2))))(str2, str3);
    }
  }
}

反编译结果是帮我们定义了几个变量。