C#的内置委托，lambda多行方法体

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//委托，不具有参数和返回值             //Action C#封装的无参数无返回值的委托             Action action = () => DateTime.Now.ToString();             action.Invoke();//同步但现场             action.BeginInvoke(null, null);//异步多线程               //委托，具有参数和返回值             //Func<T> C#封装的有参数有返回值的委托             Func<int, int, string> fun = (a, b) => DateTime.Now.Day.ToString() + $"{a}+{b}";             string result = fun.EndInvoke(fun.BeginInvoke(1, 2, null, null));               //lambda表达式,写一个方法给委托             Action action2 = () => DateTime.Now.ToString();//()代表无参，"=>"后面写方法体             //<int, int, string>除了最后一个为返回值类型，前面都是参数可多个             //(a, b)参数  //$"{a}+{b}" 字符串格式化             Func<int, int, string> fun2 = (a, b) => DateTime.Now.Day.ToString() + $"{a}+{b}";               //lambda多行方法体             Func<int, int, string> fun3 = (aa, bb) =>             {                 return DateTime.Now.Day.ToString() + $"{aa}+{bb}";             };             string result2 = fun3.EndInvoke(fun3.BeginInvoke(20, 30, null, null));//调用接收返回值