Microsoft does it again! With .Net Framework 4 Microsoft takes the C# language to new levels. In this session we will learn how to write better code using Dynamically Typed Objects, Optional & Named Parameters and Co-variance and Contra-variance.

1. What’s New in C# 4.0 Eyal Vardi CEO E4D Solutions LTDMicrosoft MVP Visual C#blog: www.eVardi.com

2. Agenda Dynamically Typed Objects Optional & Named Parameters Co- and Contra-variance

3. The Evolution of C# Dynamic C# 4.0 LINQ C# 3.0 C# 2.0 Generics C# 1.0 Managed Code

4. Dynamically Typed Objects Calculator calc = GetCalculator(); int sum = calc.Add(10, 20); object calc = GetCalculator(); TypecalcType = calc.GetType(); object res = calcType.InvokeMember("Add", BindingFlags.InvokeMethod, null, newobject[] { 10, 20 } ); int sum = Convert.ToInt32(res); Statically typed to be dynamic dynamic calc = GetCalculator(); int sum = calc.Add(10, 20); Dynamic method invocation Dynamic conversion

5. The Dynamic Type Resolved only at runtime. object  dynamic Any object can be implicitlyconverted to dynamic. dynamic  object Any dynamic Type can be assignment conversion to any other type. dynamic x = 1; // implicit conversion int num = x; // assignment conversion

6. Dynamic

7. Optional & Named Parameters

8. Improved COM Interoperability objectfileName = "Test.docx"; object missing = System.Reflection.Missing.Value; doc.SaveAs(reffileName, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing); doc.SaveAs("Test.docx");

9. Optional & Named Parameters Primary method publicStreamReaderOpenTextFile( string path, Encodingencoding, booldetectEncoding, intbufferSize); Secondary overloads publicStreamReaderOpenTextFile( string path, Encodingencoding, booldetectEncoding); publicStreamReaderOpenTextFile( string path, Encodingencoding); publicStreamReaderOpenTextFile( string path); Call primary with default values

10. Optional & Named Parameters Optional parameters publicStreamReaderOpenTextFile( string path, Encodingencoding, booldetectEncoding, intbufferSize); publicStreamReaderOpenTextFile( string path, Encodingencoding = null, booldetectEncoding = true, intbufferSize = 1024); Named argument OpenTextFile("foo.txt", Encoding.UTF8); OpenTextFile("foo.txt", Encoding.UTF8, bufferSize: 4096); Arguments evaluated in order written Named arguments can appear in any order Named arguments must be last OpenTextFile( bufferSize: 4096, path: "foo.txt", detectEncoding: false); Non-optional must be specified

11. Optional & Named Parameters

12. Co- & Contra- Variance

13. Covariance (Out) Covariance (Out):Is the ability to use a more derived type than that specified. delegateAnimal MyDel(); publicDogMethod() { ... } MyDeldel = Method; // Co - Variance (Out): Return Dog as Animal, Ok. Animalanimal = del();

14. Contra Variance (In) Contra variance (in):Is the ability to use a less derived type delegatevoidMyDel( Dogdog); publicvoidMethod(Animalanimal ){ ... } MyDeldel = Method; del( newDog() ); // Contra-Variance (In): Arg Dog as Animal, Ok.

15. Covariance & Generic What you think? IList<string> strings = new List<string>(); IList<object> objects = strings; objects[0] = 5;strings = strings[0];

16. publicinterfaceIEnumerable<T> { IEnumerator<T> GetEnumerator(); } publicinterfaceIEnumerable<out T> { IEnumerator<T> GetEnumerator(); } publicinterfaceIEnumerator<T> { T Current { get; } boolMoveNext(); } publicinterfaceIEnumerator<out T> { T Current { get; } boolMoveNext(); } Safe Covariance (Out) out= Co-variantOutput positions only Can be treated asless derived IEnumerable<string> strings = GetStrings(); IEnumerable<object> objects = strings;

17. in= Contra-variantInput positions only publicinterfaceIComparer<T> { int Compare(T x, T y); } publicinterfaceIComparer<in T> { int Compare(T x, T y); } Safe Contra Variance (In) Can be treated asmore derived objectx, y; IComparer<object> objComp = GetComparer(); objComp.Compare( x , y ); string x1, y1; IComparer<string> strComp = objComp; strComp.Compare( x1 , y1 );

18. Variance

20. Summary Dynamically Typed Objects Optional and Named Parameters Co- and Contra-variance