C #4.0 new dynamic, optional parameters, and naming Parameters

1. dynamic ExpandoObject
Anyone familiar with js knows that js can be written like this:

1 var t = new Object(); 2 t.Abc = ‘something’; 3 t.Value = 243;

We can also use this js Dynamic Language Feature in c #, provided that a variable is declared as the ExpandoObject type. For example:

1 static void Main( string [] args) 2 { 3 dynamic t = new ExpandoObject(); 4 t.Abc = "abc" ; 5 t.Value = 10000; 6 Console.WriteLine( "ts abc = {0},ts value = {1}" , t.Abc, t.Value); 7 Console.ReadLine(); 8 }

C #4.0 adds a namespace System. dynamic is used to support this application. What is the significance of this usage? I am not sure yet. It is also a test of c #'s transition to Dynamic Language.

2. Automatic generic Conversion

The following code cannot be compiled before C #4.0.

1 IEnumerable< object > objs = new List< string > { 2          "Im 0" , "Iam 1" , "Iam 2" 3      };

However, in c #4.0, this declaration is allowed, but it is also limited to generic interfaces. A similar generic method is not allowed. The following code has compilation errors:

1 List< object > objList = new List< string > {  2          "Iam 0" , "Iam 1" , "Iam 2" 3      };

3. Optional parameters of method parameters
Syntax declared in the following method

1 static void DoSomething( int notOptionalArg, string arg1 = "default Arg1" , string arg2 = "default arg2" ) { 2      Console.WriteLine( "arg1 = {0},arg2 = {1}" ,arg1,arg2); 3 }