Whats New In C# 4 0 - NetPonto
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  • The first release of C# (C# 1.0) was all about building a new language for managed code that appealed, mostly, to C++ and Java programmers.The second release (C# 2.0) was mostly about adding what wasn’t time to built into the 1.0 release. The main feature for this release was Generics.The third release (C# 3.0) was all about reducing the impedance mismatch between general purpose programming languages and databases. To achieve this goal, several functional programming features were added to the language and LINQ was born.
  • Going forward, new trends are showing up in the industry and modern programming languages need to be more:DeclarativeWith imperative languages, although having the eye on the what, programs need to focus on the how. This leads to over specification of the solution to the problem in hand, making next to impossible to the execution engine to be smart about the execution of the program and optimize it to run it more efficiently (given the hardware available, for example).Declarative languages, on the other hand, focus only on the what and leave the how to the execution engine. LINQ made C# more declarative by using higher level constructs like orderby and group by that give the execution engine a much better chance of optimizing the execution (by parallelizing it, for example).ConcurrentConcurrency is hard and needs to be thought about and it’s very hard to shoehorn it into a programming language. Parallel.For (from the parallel extensions) looks like a parallel for because enough expressiveness has been built into C# 3.0 to allow this without having to commit to specific language syntax.DynamicThere was been lots of debate on which ones are the better programming languages: static or dynamic. The fact is that both have good qualities and users of both types of languages want to have it all.All these trends require a paradigm switch. C# is, in many ways, already a multi-paradigm language. It’s still very object oriented (class oriented as some might say) but it can be argued that C# 3.0 has become a functional programming language because it has all the cornerstones of what a functional programming language needs. Moving forward, will have even more.
  • All these trends require a paradigm switch. C# is, in many ways, already a multi-paradigm language. It’s still very object oriented (class oriented as some might say) but it can be argued that C# 3.0 has become a functional programming language because it has all the cornerstones of what a functional programming language needs. Moving forward, will have even more.Besides the influence of these trends, there was a decision of co-evolution of the C# and Visual Basic programming languages. Since its inception, there was been some effort to position C# and Visual Basic against each other and to try to explain what should be done with each language or what kind of programmers use one or the other. Each language should be chosen based on the past experience and familiarity of the developer/team/project/company and not by particular features.In the past, every time a feature was added to one language, the users of the other wanted that feature too. Going forward, when a feature is added to one language, the other will work hard to add the same feature. This doesn’t mean that XML literals will be added to C# (because almost the same can be achieved with LINQ To XML), but Visual Basic will have auto-implemented properties.Most of these features require or are built on top of features of the .NET Framework and, the focus for C# 4.0 was on dynamic programming. Not just dynamic types but being able to talk with anything that isn’t a .NET class.Also introduced in C# 4.0 is co-variance and contra-variance for generic interfaces and delegates.
  • C# 4.0 (and .NET 4.0) introduced covariance and contravariance to generic interfaces and delegates. But what is this variance thing?According to Wikipedia, in multilinear algebra and tensor analysis, covariance and contravariance describe how the quantitative description of certain geometrical or physical entities changes when passing from one coordinate system to another.(*)
  • But what does this have to do with C# or .NET?In type theory, a the type T is greater (>) than type S if S is a subtype (derives from) T, which means that there is a quantitative description for types in a type hierarchy.So, how does covariance and contravariance apply to C# (and .NET) generic types?
  • In C# (and .NET), variance is a relation between a generic type definition and a particular generic type parameter.Given two types Base and Derived, such that:There is a reference (or identity) conversion between Base and DerivedBase ≥ DerivedA generic type definition Generic is:covariant in T if the ordering of the constructed types follows the ordering of the generic type parameters: Generic ≥ Generic. contravariant in T if the ordering of the constructed types is reversed from the ordering of the generic type parameters: Generic ≤ Generic. invariant in T if neither of the above apply.
  • If this definition is applied to arrays, we can see that arrays have always been covariant in relation to the type of the elements because this is valid code:object[] objectArray = new string[] { "string 1", "string 2" };objectArray[0] = "string 3";objectArray[1] = new object();However, when we try to run this code, the second assignment will throw an ArrayTypeMismatchException. Although the compiler was fooled into thinking this was valid code because an object is being assigned to an element of an array ofobject, at run time, there is always a type check to guarantee that the runtime type of the definition of the elements of the array is greater or equal to the instance being assigned to the element. In the above example, because the runtime type of the array is array of string, the first assignment of array elements is valid because string ≥ string and the second is invalid because string ≤ object.This leads to the conclusion that, although arrays have always been covariant in relation to the type of the elements, they are not safely covariant – code that compiles is not guaranteed to run without errors.
  • In C#, variance is enforced in the declaration of the type and not determined by the usage of each the generic type parameter.Covariance in relation to a particular generic type parameter is enforced, is using the out generic modifier.Notice the convenient use the pre-existing out keyword. Besides the benefit of not having to remember a new hypothetic covariant keyword, out is easier to remember because it defines that the generic type parameter can only appear in output positions — read-only properties and method return values.
  • In a similar way, the way contravariance is enforced in relation a particular generic type parameter, is using the in generic modifier.Once again, the use of the pre-existing in keyword makes it easier to remember that the generic type parameter can only be used in input positions — write-only properties and method non ref and non out parameters.
  • A generic type parameter that is not marked covariant (out) or contravariant (in) is invariant.Because covariance and contravariance applies to the relation between a generic type definition and a particular generic type parameter, a generic type definition can be both covariant, contravariant and invariant depending on the generic type parameter.In the above delegate definition, Func is contravariant in T and convariant in TResult.All the types in the .NET Framework where variance could be applied to its generic type parameters have been modified to take advantage of this new feature.In summary, the rules for variance in C# (and .NET) are:Variance in relation to generic type parameters is restricted to generic interface and generic delegate type definitions.A generic interface or generic delegate type definition can be covariant, contravariant or invariant in relation to different generic type parameters.Variance applies only to reference types: a IEnumerable is not an IEnumerable.Variance does not apply to delegate combination. That is, given two delegates of types Action and Action, you cannot combine the second delegate with the first although the result would be type safe. Variance allows the second delegate to be assigned to a variable of type Action, but delegates can combine only if their types match exactly.If you want to learn more about variance in C# (and .NET), you can always read:Covariance and Contravariance in Generics — MSDN LibraryExact rules for variance validity — Eric LippertEvents get a little overhaul in C# 4, Afterward: Effective Events — Chris BurrowsNote: Because variance is a feature of .NET 4.0 and not only of C# 4.0, all this also applies to Visual Basic 10.
  • As part of the co-evolution effort of C# and Visual Basic, C# 4.0 introduces Named and Optional Arguments.First of all, let’s clarify what are arguments and parameters:Method definition parameters are the input variables of the method.Method call arguments are the values provided to the method parameters.In fact, the C# Language Specification states the following on §7.5:The argument list (§7.5.1) of a function member invocation provides actual values or variable references for the parameters of the function member.Given the above definitions, we can state that:Parameters have always been named and still are.Parameters have never been optional and still aren’t.
  • Until now, the way the C# compiler matched method call definition arguments with method parameters was by position. The first argument provides the value for the first parameter, the second argument provides the value for the second parameter, and so on and so on, regardless of the name of the parameters. If a parameter was missing a corresponding argument to provide its value, the compiler would emit a compilation error.For this call:Greeting("Mr.", "Morgado", 42); this method:public void Greeting(string title, string name, intage)will receive as parameters:title: “Mr.”name: “Morgado”age: 42What this new feature allows is to use the names of the parameters to identify the corresponding arguments in the form: name:valueNot all arguments in the argument list must be named. However, all named arguments must be at the end of the argument list. The matching between arguments (and the evaluation of its value) and parameters will be done first by name for the named arguments and than by position for the unnamed arguments.This means that, for this method definition:public void Method(intfirst, intsecond, intthird) this call declaration:inti = 0; Method(i, third: i++, second: ++i); will have this code generated by the compiler:inti = 0; intCS$0$0000 = i++; intCS$0$0001 = ++i; Method(i, CS$0$0001, CS$0$0000); which will give the method the following parameter values:first: 2 second: 2 third: 0 Notice the variable names. Although invalid being invalid C# identifiers, they are valid .NET identifiers and thus avoiding collision between user written and compiler generated code.Besides allowing to re-order of the argument list, this feature is very useful for auto-documenting the code, for example, when the argument list is very long or not clear, from the call site, what the arguments are.
  • Parameters can now have default values:public void Method(intfirst, intsecond = 2, intthird = 3) Parameters with default values must be the last in the parameter list and its value is used as the value of the parameter if the corresponding argument is missing from the method call declaration.For this call declaration:inti = 0; Method(i, third: ++i); will have this code generated by the compiler:inti = 0; intCS$0$0000 = ++i; Method(i, 2, CS$0$0000); which will give the method the following parameter values:first: 1 second: 2 third: 1 Because, when method parameters have default values, arguments can be omitted from the call declaration, this might seem like method overloading or a good replacement for it, but it isn’t.Although methods like this:public StreamReaderOpenTextFile(string path,Encoding encoding = null,booldetectEncoding = true,intbufferSize = 1024) allow to have its calls written like this:OpenTextFile("foo.txt", Encoding.UTF8); OpenTextFile("foo.txt", Encoding.UTF8, bufferSize: 4096); OpenTextFile(bufferSize: 4096, path: "foo.txt",detectEncoding: false); The complier handles default values like constant fields taking the value and useing it instead of a reference to the value. So, like with constant fields, methods with parameters with default values are exposed publicly (and remember that internal members might be publicly accessible – InternalsVisibleToAttribute). If such methods are publicly accessible and used by another assembly, those values will be hard coded in the calling code and, if the called assembly has its default values changed, they won’t be assumed by already compiled code.At the first glance, I though that using optional arguments for “bad” written code was great, but the ability to write code like that was just pure evil. But than I realized that, since I use private constant fields, it’s OK to use default parameter values on privately accessed methods.
  • Like I mentioned in my last post, exposing publicly methods with optional arguments is a bad practice (that’s why C# has resisted to having it, until now).You might argument that your method or constructor has to many variants and having ten or more overloads is a maintenance nightmare, and you’re right. But the solution has been there for ages: have an arguments class.The arguments class pattern is used in the .NET Framework is used by several classes, like XmlReader and XmlWriter that use such pattern in their Create methods, since version 2.0:XmlReaderSettingssettings = new XmlReaderSettings(); settings.ValidationType = ValidationType.Auto; XmlReader.Create("file.xml", settings); With this pattern, you don’t have to maintain a long list of overloads and any default values for properties of XmlReaderSettings (or XmlWriterSettings for XmlWriter.Create) can be changed or new properties added in future implementations that won’t break existing compiled code.You might now argue that it’s too much code to write, but, with object initializers added in C# 3.0, the same code can be written like this:XmlReader.Create("file.xml", new XmlReaderSettings{ ValidationType = ValidationType.Auto }); Looks almost like named and optional arguments, doesn’t it? And, who knows, in a future version of C#, it might even look like this:XmlReader.Create("file.xml", new { ValidationType = ValidationType.Auto });
  • The major feature of C# 4.0 is dynamic programming. Not just dynamic typing, but dynamic in broader sense, which means talking to anything that is not statically typed to be a .NET object.Dynamic Language RuntimeThe Dynamic Language Runtime (DLR) is piece of technology that unifies dynamic programming on the .NET platform, the same way the Common Language Runtime (CLR) has been a common platform for statically typed languages.The CLR always had dynamic capabilities. You could always use reflection, but its main goal was never to be a dynamic programming environment and there were some features missing. The DLR is built on top of the CLR and adds those missing features to the .NET platform.The Dynamic Language Runtime is the core infrastructure that consists of:Expression TreesThe same expression trees used in LINQ, now improved to support statements.Dynamic DispatchDispatches invocations to the appropriate binder.Call Site CachingFor improved efficiency.Dynamic languages and languages with dynamic capabilities are built on top of the DLR. IronPython and IronRuby were already built on top of the DLR, and now, the support for using the DLR is being added to C# and Visual Basic. Other languages built on top of the CLR are expected to also use the DLR in the future.Underneath the DLR there are binders that talk to a variety of different technologies:.NET BinderAllows to talk to .NET objects.JavaScript BinderAllows to talk to JavaScript in SilverLight.IronPython BinderAllows to talk to IronPython.IronRuby BinderAllows to talk to IronRuby.COM BinderAllows to talk to COM.Whit all these binders it is possible to have a single programming experience to talk to all these environments that are not statically typed .NET objects.
  • Let’s take this traditional statically typed code:Calculator calculator = GetCalculator(); intsum = calculator.Sum(10, 20); Because the variable that receives the return value of the GetCalulator method is statically typed to be of type Calculator and, because the Calculator type has an Add method that receives two integers and returns an integer, it is possible to call that Sum method and assign its return value to a variable statically typed as integer.Now lets suppose the calculator was not a statically typed .NET class, but, instead, a COM object or some .NET code we don’t know he type of. All of the sudden it gets very painful to call the Add method:object calculator = GetCalculator(); Type calculatorType = calculator.GetType(); object res = calculatorType.InvokeMember("Add", BindingFlags.InvokeMethod, null, calculator, new object[] { 10, 20 }); intsum = Convert.ToInt32(res); And what if the calculator was a JavaScript object?ScriptObjectcalculator = GetCalculator(); object res = calculator.Invoke("Add", 10, 20); intsum = Convert.ToInt32(res); For each dynamic domain we have a different programming experience and that makes it very hard to unify the code.With C# 4.0 it becomes possible to write code this way:dynamic calculator = GetCalculator(); intsum = calculator.Add(10, 20); You simply declare a variable who’s static type is dynamic. dynamic is a pseudo-keyword (like var) that indicates to the compiler that operations on the calculator object will be done dynamically.The way you should look at dynamic is that it’s just like object (System.Object) with dynamic semantics associated. Anything can be assigned to a dynamic.
  • At run-time, all object will have a type. In the above example x is of type System.Int32.When one or more operands in an operation are typed dynamic, member selection is deferred to run-time instead of compile-time. Then the run-time type is substituted in all variables and normal overload resolution is done, just like it would happen at compile-time.
  • The result of any dynamic operation is always dynamic and, when a dynamic object is assigned to something else, a dynamic conversion will occur.double x = 1.75; double y = Math.Abs(x);Compile-timedouble Abs(double x)dynamic x = 1.75; dynamic y = Math.Abs(x);Run-timedouble Abs(double x)dynamic x = 2; dynamic y = Math.Abs(x);Run-timeint Abs(int x)The above code will always be strongly typed. The difference is that, in the first case the method resolution is done at compile-time, and the others it’s done ate run-time.
  • The DLR is pre-wired to know .NET objects, COM objects and so forth but any dynamic language can implement their own objects or you can implement your own objects in C# through the implementation of the IDynamicMetaObjectProvider interface. When an object implements IDynamicMetaObjectProvider, it can participate in the resolution of how method calls and property access is done.The .NET Framework already provides two implementations of IDynamicMetaObjectProvider:DynamicObject : IDynamicMetaObjectProviderThe DynamicObject class enables you to define which operations can be performed on dynamic objects and how to perform those operations. For example, you can define what happens when you try to get or set an object property, call a method, or perform standard mathematical operations such as addition and multiplication.ExpandoObject : IDynamicMetaObjectProviderThe ExpandoObject class enables you to add and delete members of its instances at run time and also to set and get values of these members. This class supports dynamic binding, which enables you to use standard syntax like sampleObject.sampleMember, instead of more complex syntax like sampleObject.GetAttribute("sampleMember").
  • Dynamic resolution as well as named and optional arguments greatly improve the experience of interoperating with COM APIs such as Office Automation Primary Interop Assemblies (PIAs). But, in order to alleviate even more COMInterop development, a few COM-specific features were also added to C# 4.0.
  • Because of a different programming model, many COM APIs contain a lot of reference parameters. These parameters are typically not meant to mutate a passed-in argument, but are simply another way of passing value parameters.Specifically for COM methods, the compiler allows to declare the method call passing the arguments by value and will automatically generate the necessary temporary variables to hold the values in order to pass them by reference and will discard their values after the call returns. From the point of view of the programmer, the arguments are being passed by value.
  • Dynamic ImportMany COM methods accept and return variant types, which are represented in the PIAs as object. In the vast majority of cases, a programmer calling these methods already knows the static type of a returned object form the context of the call, but has to explicitly perform a cast on the returned values to make use of that knowledge. These casts are so common that they constitute a major nuisance.To make the developer’s life easier, it is now possible to import the COM APIs in such a way that variants are instead represented using the type dynamic which means that COM signatures have now occurrences of dynamic instead of object.This means that members of a returned object can now be easily accessed or assigned into a strongly typed variable without having to cast.Indexed And Default PropertiesA few COM interface features are still not available in C#. On the top of the list are indexed properties and default properties. As mentioned above, these will be possible if the COM interface is accessed dynamically, but will not be recognized by statically typed C# code.
  • For assemblies indentified with PrimaryInteropAssemblyAttribute, the compiler will create equivalent types (interfaces, structs, enumerations and delegates) and embed them in the generated assembly.To reduce the final size of the generated assembly, only the used types and their used members will be generated and embedded.Although this makes development and deployment of applications using the COM components easier because there’s no need to deploy the PIAs, COM component developers are still required to build the PIAs.

Whats New In C# 4 0 - NetPonto Presentation Transcript

  • 1. What's New In C# 4.0
  • 2. Paulo Morgado
  • 3. The Evolution Of C#
    Covariance And Contravariance
    Named And Optional Arguments
    Dynamic Programming
    COM Interop Improvements
    Agenda
  • 4. The Evolution Of C#
  • 5. The Evolution Of C#
  • 6. Trends
  • 7. Dynamic vs. Static
  • 8. VB
    • Named Arguments
    • 9. Optional Arguments
    • 10. Index Properties (COM)
    • 11. Lambda Statements
    • 12. Auto-Implemented Properties
    • 13. Colection Initializers
    C#
    C#
    VB
    Co-Evolution
  • 14. The Evolution Of C#
  • 15. The Evolution Of C#
    http://paulomorgado.net/en/blog/archive/2010/04/12/the-evolution-of-c.aspx
    Resources
  • 16. Covariance And Contravariance
  • 17. In multilinear algebra and tensor analysis, covariance and contravariance describe how the quantitative description of certain geometrical or physical entities changes when passing from one coordinate system to another.
    Wikipedia
    Covariance And Contravarance
  • 18. Type Tis greater than (>) type Sif Sis a subtype of (derives from) T
    Covariance And Contravarance
    T≥S
    typeof(T).IsAssignableFrom(typeof(S))
  • 19. Give 2 types Base and Derived, such that:
    There is a reference (or identity) conversion between Base and Derived
    Base ≥ Derived
    A generic type definition Generic<T> is:
    Covariant in T
    If Genérico<Base> ≥ Genérico<Derived>
    Contravariant in T
    If Genérico<Base> ≤ Genérico<Derived>
    Invariant in T
    If neither of the above apply
    Covariance And Contravarance
  • 20. Contravariante em T
    Covariante em T
    typeof(Base).IsAssignableFrom(typeof(Derived))
    typeof(Base).IsAssignableFrom(typeof(Derived))
    typeof(G<Derived>).IsAssignableFrom(typeof(G<Base>))
    typeof(G<Base>).IsAssignableFrom(typeof(G<Derived>))
    Covariance And Contravarance
  • 21. Covariance And Contravarance
    C# (.NET) arrays are covariant
    string[] strings = GetStringArray();
    Process(strings);
    … but not safely covariant
    void Process(object[] objects) { … }
    void Process(object[] objects)
    {
    objects[0] = "Hello"; // Ok
    objects[1] = newButton(); // Exception!
    }
  • 22. Covariance And Contravarance
    Until now, C# (.NET) generics have been invariant
    List<string> strings = GetStringList();
    Process(strings);
    C# 4.0 supports safe covariance and contravariance
    void Process(IEnumerable<object> objects)
    {
    // IEnumerable<T> is read-only and
    // therefore safely covariant
    }
    void Process(IEnumerable<object> objects) { … }
  • 23. Safe Covariance
    out= covariant
    Output positions only
    publicinterfaceIEnumerable<T>
    {
    IEnumerator<T> GetEnumerator();
    }
    publicinterfaceIEnumerable<out T>
    {
    IEnumerator<T> GetEnumerator();
    }
    Can be treated as less derived
    publicinterfaceIEnumerator<T>
    {
    T Current { get; }
    boolMoveNext();
    }
    publicinterfaceIEnumerator<out T>
    {
    T Current { get; }
    boolMoveNext();
    }
    IEnumerable<string> strings = GetStrings();
    IEnumerable<object> objects = strings;
  • 24. Safe Contravariance
    in= contravariantInput positions only
    Can be treated as more derived
    publicinterfaceIComparer<T>
    {
    int Compare(T x, T y);
    }
    publicinterfaceIComparer<in T>
    {
    int Compare(T x, T y);
    }
    IComparer<object> objComp = GetComparer();
    IComparer<string> strComp = objComp;
  • 25. Supported for generic interface and delegate types only.
    Verified/enforced staticaliy in the definition.
    Value types are always invariant
    IEnumerable<int> is not IEnumerable<object>
    Similar to existing rules for arrays
    ref and out parameters need invariant types
    Variance In C# 4.o
  • 26. Variance In .NET 4.0
  • 27. Covariance And Contravariance In Generics
    http://paulomorgado.net/en/blog/archive/2010/04/13/c-4-0-covariance-and-contravariance-in-generics.aspx
    Covariance And Contravariance In Generics Made Easy
    http://paulomorgado.net/en/blog/archive/2010/04/15/c-4-0-covariance-and-contravariance-in-generics-made-easy.aspx
    Covarince and Contravariance in Generics
    http://msdn.microsoft.com/library/dd799517(VS.100).aspx
    Exact rules for variance validity
    http://blogs.msdn.com/ericlippert/archive/2009/12/03/exact-rules-for-variância-validity.aspx
    Events get a little overhaul in C# 4, Afterward: Effective Events
    http://blogs.msdn.com/cburrows/archive/2010/03/30/events-get-a-little-overhaul-in-c-4-afterward-effective-events.aspx
    Resources
  • 28. Named And Optional Arguments
  • 29. Named And Optional Arguments
    Greeting("Mr.", "Morgado", 42);
    Parameters
    Arguments
    public void Greeting(string title, string name, intage)
    They always have names
    They are never optional
  • 30. Named Arguments
    int i = 0;
    Method(i, third: i++, second: ++i);
    int i = 0;
    int CS$0$0000 = i++;
    int CS$0$0001 = ++i;
    Method(i, CS$0$0001, CS$0$0000);
    public void Method(intfirst, intsecond, intthird)
  • 31. Optional Arguments
    int i = 0;
    Method(i, third: ++i);
    int i = 0;
    int CS$0$0000 = ++i;
    Method(i, 2, CS$0$0000);
    public void Method(intfirst, intsecond = 5, intthird = 6)
    public void Method(intfirst, intsecond = 2, intthird = 3)
    public void Method(intfirst, intsecond)
    They look like overloads.
    But they aren’t!
    public void Method(intfirst)
  • 32. Argument Classes
    Optional Arguments - Alternative
    XmlReaderSettings settings = newXmlReaderSettings();
    settings.ValidationType = ValidationType.Auto;
    XmlReader.Create("file.xml", settings);
    XmlReader.Create(
    "file.xml",
    new { ValidationType = ValidationType.Auto });
    XmlReader.Create(
    "file.xml",
    newXmlReaderSettings { ValidationType = ValidationType.Auto });
    Not yet!
  • 33. C# 4.0: Named And Optional Arguments
    http://paulomorgado.net/en/blog/archive/2010/04/16/c-4-0-named-and-optional-arguments.aspx
    C# 4.0: Alternative To Optional Arguments
    http://paulomorgado.net/en/blog/archive/2010/04/18/c-4-0-alternative-to-optional-arguments.aspx
    Named and Optional Arguments (C# Programming Guide)
    http://msdn.microsoft.com/library/dd264739(VS.100).aspx
    Resources
  • 34. Dynamic Programming
  • 35. Dynamic Language Runtime
    IronPython
    IronRuby
    C#
    VB.NET
    Others…
    Dynamic Language Runtime
    Expression Trees
    Dynamic Dispatch
    Call Site Caching
    PythonBinder
    RubyBinder
    COMBinder
    JavaScriptBinder
    ObjectBinder
  • 36. Objectos Tipados Dinâmicamente
    Calculatorcalculator = GetCalculator();
    int sum = calc.Add(10, 20);
    object calculator = GetCalculator();
    Type calculatorType = calculator.GetType();
    object res = calculatorType.InvokeMember("Add",
    BindingFlags.InvokeMethod, null,
    calculator, newobject[] { 10, 20 });
    int sum = Convert.ToInt32(res);
    ScriptObject calculator = GetCalculator();
    object res = calculator.Invoke("Add", 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
  • 37. Dynamically Typed Objects
    Compile-time typedynamic
    Run-time typeSystem.Int32
    dynamic x = 1;
    dynamic y = "Hello";
    dynamic z = newList<int> { 1, 2, 3 };
    When operand(s) are dynamic:
    • Member selection deferred to run-time
    • 38. At run-time, actual type(s) substituted for dynamic
    • 39. Static result type of operation is dynamic
  • Dynamically Typed Objects
    public 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);
    ...
    }
    Method chosen at compile-time:double Abs(double x)
    double x = 1.75;
    double y = Math.Abs(x);
    Method chosen at
    run-time:double Abs(double x)
    dynamic x = 1.75;
    dynamic y = Math.Abs(x);
    Method chosen at
    run-time:int Abs(int x)
    dynamic x = 2;
    dynamic y = Math.Abs(x);
  • 40. IDynamicMetaObjectProvider
    Represents a dynamic object that can have operations determined at run-time.
    DynamicObject : IDynamicMetaObjectProvider
    Enables you to define which operations can be performed on dynamic objects and how to perform those operations.
    ExpandoObject : IDynamicMetaObjectProvider
    Enables you to add and delete members of its instances at run time and also to set and get values of these members.
    Building Dynamic Objects
  • 41. Dynamic Programming
    http://paulomorgado.net/en/blog/archive/2010/04/18/c-4-0-dynamic-programming.aspx
    C# Proposal: Compile Time Static Checking Of Dynamic Objects
    http://paulomorgado.net/en/blog/archive/2010/03/19/c-proposal-compile-time-static-checking-of-dynamic-objects.aspx
    Using Type dynamic (C# Programming Guide)
    http://msdn.microsoft.com/library/dd264736(VS.100).aspx
    Dynamic Language Runtime Overview
    http://msdn.microsoft.com/library/dd233052(v=VS.100).aspx
    Resources
  • 42. COM Interop Improvements
  • 43. Named and optional arguments
    Ommiting ref
    Dynamic Import
    Automatic mapping object -> dynamic
    Indexed properties
    Type Equivalence And Type Embedding (“NO PIA”)
    COM Interop Improvements
  • 44. Ommiting ref
    objectfileName = "Test.docx";
    object missing = Missing.Value;
    document.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);
    document.SaveAs("Test.docx",
    Missing.Value, Missing.Value, Missing.Value,
    Missing.Value, Missing.Value, Missing.Value,
    Missing.Value, Missing.Value, Missing.Value,
    Missing.Value, Missing.Value, Missing.Value,
    Missing.Value, Missing.Value, Missing.Value);
    document.SaveAs("Test.docx");
  • 45. Dynamic Import
    ((Excel.Range)(excel.Cells[1, 1])).Value2 = "Hello World!";
    excel.Cells[1, 1] = "Hello World!";
    Excel.Range range = (Excel.Range)(excel.Cells[1, 1]);
    Excel.Rangerange = excel.Cells[1, 1];
  • 46. Type Equivalence And Type Embedding (NO PIA)
  • 47. COM Interop Improvements
    http://paulomorgado.net/en/blog/archive/2010/04/19/c-4-0-com-interop-improvements.aspx
    Type Equivalence and Embedded InteropTypes
    http://msdn.microsoft.com/library/dd997297.aspx
    Resources
  • 48. Demos
  • 49.
  • 50. Conclusion
  • 51. The Evolution Of C#
    Covariance And Contravariance
    Named And Optional Arguments
    Dynamic Programming
    COM Interop Improvements
    Conclusion
  • 52. Visual C# Developer Center
    http://csharp.net/
    Visual C# 2010 Samples
    http://code.msdn.microsoft.com/cs2010samples
    C# Language Specification 4.0
    http://www.microsoft.com/downloads/details.aspx?familyid=DFBF523C-F98C-4804-AFBD-459E846B268E&displaylang=en
    Resources
  • 53. .NET Reflector
    http://www.red-gate.com/products/reflector/
    LINQPad
    http://linqpad.net/
    Paulo Morgado
    http://PauloMorgado.NET/
    Resources
  • 54. Thank You!