The document summarizes the evolution and future directions of the C# programming language. It discusses new features in recent versions such as generics in C# 2.0, language integrated query in C# 3.0, and dynamic programming in C# 4.0. It also covers trends toward declarative programming, concurrency, and compiler as a service. The presentation provides examples and demos of new C# 4.0 features like dynamic typing, optional and named parameters, and covariance and contravariance.

1. The Future of C#TL16 Anders Hejlsberg Technical Fellow Microsoft Corporation

2. The Evolution of C#C# 3.0Language Integrated QueryC# 2.0GenericsC# 1.0Managed Code

3. Trends

4. Declarative ProgrammingWhatHowImperativeDeclarative

5. Dynamic vs. Static

6. Concurrency

7. Co-Evolution

8. The Evolution of C#C# 4.0Dynamic ProgrammingC# 3.0Language Integrated QueryC# 2.0GenericsC# 1.0Managed Code

9. Dynamically Typed ObjectsOptional and Named ParametersImproved COM InteroperabilityCo- and Contra-varianceC# 4.0 Language Innovations

10. .NET Dynamic ProgrammingIronPythonIronRubyC#VB.NETOthers…Dynamic Language RuntimeExpression TreesDynamic DispatchCall Site CachingPythonBinderRubyBinderCOMBinderJavaScriptBinderObjectBinder

11. Dynamically Typed ObjectsCalculator 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);ScriptObject calc = GetCalculator();object res = calc.Invoke("Add", 10, 20);int sum = Convert.ToInt32(res);Statically typed to be dynamicdynamic calc = GetCalculator();int sum = calc.Add(10, 20);Dynamic method invocationDynamic conversion

12. Dynamically Typed ObjectsCompile-time typedynamicRun-time typeSystem.Int32dynamic x = 1;dynamic y = "Hello";dynamic z = newList<int> { 1, 2, 3 };When operand(s) are dynamic… Member selection deferred to run-time

13. At run-time, actual type(s) substituted for dynamic

14. Static result type of operation is dynamicpublic static class Math{ publicstaticdecimal Abs(decimal value); publicstaticdouble Abs(double value); publicstaticfloat Abs(float value); publicstaticint Abs(int value); publicstaticlong Abs(long value); publicstaticsbyte Abs(sbyte value); publicstaticshort Abs(short value); ...}double x = 1.75;double y = Math.Abs(x);dynamic x = 1.75;dynamic y = Math.Abs(x);Dynamically Typed ObjectsMethod chosen at compile-time:double Abs(double x)Method chosen at run-time: double Abs(double x)Method chosen at run-time:int Abs(int x)dynamic x = 2;dynamic y = Math.Abs(x);

15. Dynamically Typed Objectsdemo

16. IDynamicObjectpublicabstractclassDynamicObject : IDynamicObject{publicvirtualobjectGetMember(GetMemberBinder info);publicvirtualobjectSetMember(SetMemberBinder info, object value);publicvirtualobjectDeleteMember(DeleteMemberBinder info); publicvirtualobjectUnaryOperation(UnaryOperationBinder info);publicvirtualobjectBinaryOperation(BinaryOperationBinder info, objectarg);publicvirtualobject Convert(ConvertBinder info); publicvirtualobject Invoke(InvokeBinder info, object[] args);publicvirtualobjectInvokeMember(InvokeMemberBinder info, object[] args);publicvirtualobjectCreateInstance(CreateInstanceBinder info, object[] args); publicvirtualobjectGetIndex(GetIndexBinder info, object[] indices);publicvirtualobjectSetIndex(SetIndexBinder info, object[] indices, object value);publicvirtualobjectDeleteIndex(DeleteIndexBinder info, object[] indices); publicMetaObjectIDynamicObject.GetMetaObject();}

17. Implementing IDynamicObjectdemo

18. Optional and Named ParametersPrimary methodpublicStreamReaderOpenTextFile( string path, Encodingencoding,booldetectEncoding,intbufferSize);Secondary overloadspublicStreamReaderOpenTextFile( string path, Encodingencoding,booldetectEncoding);publicStreamReaderOpenTextFile( string path, Encodingencoding);publicStreamReaderOpenTextFile( string path);Call primary with default values

19. Optional and Named ParametersOptional parameterspublicStreamReaderOpenTextFile( string path, Encodingencoding,booldetectEncoding,intbufferSize);publicStreamReaderOpenTextFile( string path, Encodingencoding = null,booldetectEncoding = true,intbufferSize = 1024);Named argumentOpenTextFile("foo.txt", Encoding.UTF8);OpenTextFile("foo.txt", Encoding.UTF8, bufferSize: 4096);Arguments evaluated in order writtenNamed arguments can appear in any orderNamed arguments must be lastOpenTextFile(bufferSize: 4096, path: "foo.txt",detectEncoding: false);Non-optional must be specified

20. Improved COM InteroperabilityobjectfileName = "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");

21. Automatic object  dynamic mappingOptional and named parametersIndexed propertiesOptional “ref” modifierInterop type embedding (“No PIA”)Improved COM Interoperability

22. Improved COM Interoperabilitydemo

23. Co- and Contra-variance.NET arrays are co-variantstring[] strings = GetStringArray();Process(strings);…but not safelyco-variantvoid Process(object[] objects) { … }void Process(object[] objects) { objects[0] = "Hello"; // Ok objects[1] = newButton(); // Exception!}Until now, C# generics have been invariantList<string> strings = GetStringList();Process(strings);C# 4.0 supports safe co- and contra-variancevoid Process(IEnumerable<object> objects) { … }void Process(IEnumerable<object> objects) {// IEnumerable<T> is read-only and// therefore safely co-variant}

24. Safe Co- and Contra-variancepublicinterfaceIEnumerable<T>{IEnumerator<T> GetEnumerator();}publicinterfaceIEnumerable<out T>{IEnumerator<T> GetEnumerator();}out= Co-variantOutput positions onlyCan be treated asless derivedpublicinterfaceIEnumerator<T>{ T Current { get; }boolMoveNext();}publicinterfaceIEnumerator<out T>{ T Current { get; }boolMoveNext();}IEnumerable<string> strings = GetStrings();IEnumerable<object> objects = strings;in= Contra-variantInput positions onlypublicinterfaceIComparer<T>{int Compare(T x, T y);}publicinterfaceIComparer<in T>{int Compare(T x, T y);}Can be treated asmore derivedIComparer<object> objComp = GetComparer();IComparer<string> strComp = objComp;

25. Variance in C# 4.0Supported for interface and delegate types“Statically checked definition-site variance”Value types are always invariantIEnumerable<int> is not IEnumerable<object>Similar to existing rules for arraysref and out parameters need invariant type

26. Variance in .NET Framework 4.0InterfacesSystem.Collections.Generic.IEnumerable<out T>System.Collections.Generic.IEnumerator<out T>System.Linq.IQueryable<out T>System.Collections.Generic.IComparer<in T>System.Collections.Generic.IEqualityComparer<in T>System.IComparable<in T>DelegatesSystem.Func<in T, …, out R>System.Action<in T, …>System.Predicate<in T>System.Comparison<in T>System.EventHandler<in T>

27. The Evolution of C#C# 4.0Dynamic ProgrammingC# 3.0Language Integrated QueryC# 2.0GenericsC# 1.0Managed Code

28. Compiler as a ServiceClassMeta-programmingRead-Eval-Print LooppublicFooFieldLanguageObject ModelDSL EmbeddingprivateXstringCompilerCompilerSourceFile.NET AssemblySource codeSource codeSource codeSource code

29. Compiler as a Servicedemo

30. Book SigningBookstoreMonday3:30 PM

31. Related SessionsTL10: Deep Dive: Dynamic Languages in .NETTL54: Natural Interop with Silverlight, Office, …TL12: Future Directions for Microsoft Visual BasicTL57: Panel: The Future of Programming LanguagesTL11: An Introduction to Microsoft F#C# 4.0 Samples and Whitepaperhttp://code.msdn.microsoft.com/csharpfutureVisual C# Developer Centerhttp://csharp.netAdditional Resources

32. Evals & RecordingsPlease fill out your evaluation for this session at:This session will be available as a recording at:www.microsoftpdc.com

33. Please use the microphones providedQ&A

34. © 2008 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.