What’s new in Visual Studio 2010 and C# 4.0

Kirill OsenkovVisual Studio C# IDE Team

Language Features in C# 4.0

1. Dynamic2. Co-/Contravariance3. Named and Optional Arguments4. COM Interop Improvements

1. Dynamic – Late Binding in C#

Early binding:Console.WriteLine();

Late binding:typeof(Console).GetMethod("WriteLine").Invoke(null, null);

Static typing• Compiler checks members and types• IDE IntelliSense• Binding at compile time, exact

method baked into ILcall void [mscorlib]System.Console::WriteLine()

Dynamic typing• Member names, types and signatures

not known at compile time• JavaScript, IronPython, IronRuby• COM Interop Scenarios• Reflection over non-accessible types• Compiler can’t check correctness• Refactoring doesn’t work

Starting Visual Studio// Type is not known at compile timeType vsType = Type.GetTypeFromProgID("VisualStudio.Dte.10.0");

// create an instance dynamicallyobject instance = Activator.CreateInstance(vsType);

// get the property and hope it's therePropertyInfo property = vsType.GetProperty("Visible");

// call and pass weakly typed argumentsproperty.SetValue(instance, true, null);

Information in the code:// Type is not known at compile timeType vsType = Type.GetTypeFromProgID("VisualStudio.Dte.10.0");

// create an instance dynamicallyobject instance = Activator.CreateInstance(vsType);

// get the property and hope it's therePropertyInfo property = vsType.GetProperty("Visible");

// call and pass weakly typed argumentsproperty.SetValue(instance, true, null);

Information in the code:• In this object, set the ‘Visible’

property to trueobject

instance

SetProperty

Name: ‘Visible’

Value: ‘true’

Expressing call information in codeType vsType = Type.GetTypeFromProgID("VisualStudio.Dte.10.0");

BEFORE:

object instance = Activator.CreateInstance(vsType);PropertyInfo property = vsType.GetProperty("Visible");property.SetValue(instance, true, null);

AFTER:

dynamic instance = Activator.CreateInstance(vsType);instance.Visible = true;

How it works

instance.Visible = true;

How it works

… becomes …

How it worksif (<StartVSDynamic>o__SiteContainer0.<>p__Site1 == null){ <StartVSDynamic>o__SiteContainer0.<>p__Site1 = CallSite<Func<CallSite, object, bool, object>>.Create(Binder.SetMember(CSharpBinderFlags.None, "Visible", typeof(Program), new CSharpArgumentInfo[] { CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null), CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.Constant | CSharpArgumentInfoFlags.UseCompileTimeType, null) }));}<StartVSDynamic>o__SiteContainer0.<>p__Site1.Target.Invoke(<StartVSDynamic>o__SiteContainer0.<>p__Site1, instance, true);

Details• A DLR callsite object is created upon

first request• All the statically known callsite

information is encapsulated• Callsites are cached for performance

Bonus abstraction layer• A way to intercept dynamic calls and

plug in your own behavior• DynamicObject,

IDynamicMetaObjectProvider• TryGetMember, TrySetMember get

called when a member is called on the dynamic object

• ExpandoObject

Dynamic sample: Dictionarycolors.Blueinstead ofcolors["Blue"]

colors.Red = 0xFF0000;instead ofcolors.Add("Red", 0xFF0000);

Dynamic sample: XMLcustomer.Address.Street

instead ofcustomer.Element(“Address”).Attribute(“Street”).Value

Dynamic sample: XMLdynamic contact = new DynamicXMLNode("Contacts");contact.Name = "Patrick Hines";contact.Phone = "206-555-0144";contact.Address = new DynamicXMLNode();contact.Address.Street = "123 Main St";contact.Address.City = "Mercer Island";contact.Address.State = "WA"; contact.Address.Postal = "68402";

Dynamic Sample: Reflection• Before:var employee = new Employee();var members = employee.GetType().GetMember("age",     MemberTypes.All,     BindingFlags.IgnoreCase     | BindingFlags.Instance     | BindingFlags.NonPublic     | BindingFlags.Public);((FieldInfo)members[0]).SetValue(employee, 42);

• After:dynamic employee = (new Employee()).AsDynamic();employee.Age = 42;

2. Co/Contravariance• This feature is very hard to explain• You only need it once a month or less• When you do need it you do need it• It’s about passing around generic

interfaces and delegates only• Whatever you’d expect should work

now works

IN and OUT:

public Widget CreateWidget(string name);

“IN”“OUT”

Fails in C# 3:using System;

class Program{ static void Main(string[] args) { Func<string> stringFactory = () => "Hello"; Print(stringFactory); }

static void Print(Func<object> objectFactory) { object o = objectFactory(); Console.WriteLine(o); }}

Works in C# 4:using System;

class Program{ static void Main(string[] args) { Func<string> stringFactory = () => "Hello"; Print(stringFactory); }

static void Print(Func<object> objectFactory) { object o = objectFactory(); Console.WriteLine(o); }}

string

object

Func<string>

Func<object>

covariance

out == covariant

• Func is covariant in TResult• All about “producing” types• Func<T>, IEnumerable<T>, *Factory, *Creator

• Covariant interfaces and delegates in the BCL are annotated with ‘out’

public delegate TResult Func<out TResult>();

Fails in C# 3:using System;

class Program{ static void Main(string[] args) { Action<object> objectPrinter = Console.WriteLine; PrintHello(objectPrinter); }

static void PrintHello(Action<string> printer) { printer("Hello"); }}

Works in C# 4:using System;

class Program{ static void Main(string[] args) { Action<object> objectPrinter = Console.WriteLine; PrintHello(objectPrinter); }

static void PrintHello(Action<string> printer) { printer("Hello"); }}

string

object

Action<string>

Action<object>

contravariance

in == contravariant

• Action is contravariant in T• All about “consuming” types: Action<T>, IComparer<T>

• Contravariant interfaces and delegates in the BCL are annotated with ‘in’

public delegate void Action<in T>(T obj);

Co/Contravariant BCL Types• Covariance (“out”):– IEnumerable<Animal> is now assignable

from IEnumerable<Cat>– Func<Cat> is now also a Func<Animal>

• Contravariance (“in”):– A variable of type Action<Cat> (specific)

can now be assigned a value of type Action<Animal>(generic)

• http://msdn.microsoft.com/en-us/library/dd799517.aspx

Named argumentsdocument.Close(saveChanges: true);vs.document.Close(true);

• Arguments can now be specified out of order

• Code readability is improved• Warning: parameter names become part of API• Renaming a parameter in one assembly can

now break the code in another assembly

Optional arguments• Before:var app = new Application();var missing = Type.Missing;object fileName = "word.doc";app.Documents.Open(    ref fileName, 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);

Optional arguments• After:var app = new Application();app.Documents.Open("word.doc");

COM improvements1. Omit ref2. No PIA3. Indexed properties

Omit ref on COM arguments• app.Documents.Close(missing);

instead of• app.Documents.Close(ref missing);

No PIA (Primary Interop Assemblies)

• PIAs are managed wrapper assemblies around COM types: EnvDTE, Microsoft.Office.Interop.Word, etc.

• Can embed the necessary parts in your program

• PIA doesn’t need to be distributed with your app

No PIA (Primary Interop Assemblies)

Indexed Properties• Before:

excel.get_Range("A1").set_Value(Type.Missing, "ID");

• After:excel.Range["A1"].Value = "ID";

Event implementation changes

• Before:[MethodImpl(MethodImplOptions.Synchronized)]public void add_MouseDown(Action value){ this.MouseDown =

(Action) Delegate.Combine(this.MouseDown, value);}

Event implementation changes

• After:public static void add_MouseDown(Action value){ Action action2; Action MouseDown = MouseDown; do { action2 = MouseDown; Action action3 =

(Action) Delegate.Combine(action2, value); MouseDown = Interlocked.CompareExchange<Action>

(ref MouseDown, action3, action2); } while (MouseDown != action2);}

C# IDE Features

C# IDE Features• Ctrl+,• Ctrl+K,T• Ctrl+Shift+Up/Down• Ctrl+.• Ctrl+Alt+Space

C# IDE Features• Navigate To• Call Hierarchy• Highlight References• Generate From Usage• IntelliSense improvements (consume-

first, sub-string and camelCase search)

Q & A• Kirill Osenkov• http://blogs.msdn.com/b/kirillosenkov• http://twitter.com/kirillosenkov

Bonus slides

Team Architect• Architecture Explorer• Sequence Diagrams• DGML – graph modeling

Debugger• IntelliTrace• Pinnable Data Tips• Thread Window improvements

(Freeze/thaw)• Parallel Debugging tool windows

Shell• WPF Shell• Multi-monitor support• Extension Manager

Editor• Brand new WPF text editor• Box-selection• Zoom, Ctrl+scroll

Shameless Plug:• My open-source projects:• http://livegeometry.codeplex.com• http://undo.codeplex.com• http://structurededitor.codeplex.com• http://layout.osenkov.com