What's New in C# 3.0? What's New in C# 3.0?

Clint EdmonsonClint EdmonsonArchitect EvangelistArchitect EvangelistMicrosoft CorporationMicrosoft Corporationwww.notsotrivial.net www.notsotrivial.net

AgendaAgenda

C# Design ThemesC# Design Themes

New Features in ActionNew Features in Action

SummarySummary

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QuestionsQuestions

C# 3.0 - Design ThemesC# 3.0 - Design Themes

Improves on C# 2.0Improves on C# 2.0

100% Backwards Compatible100% Backwards Compatible

Language Integrated Query (LINQ)Language Integrated Query (LINQ)

New Features in ActionNew Features in Action

New Features in C# 3.0 New Features in C# 3.0

Local Variable Type InferenceLocal Variable Type Inference

Object InitializersObject Initializers

Collection InitializersCollection Initializers

Anonymous TypesAnonymous Types

Auto-Implemented PropertiesAuto-Implemented Properties

Extension MethodsExtension Methods

LambdasLambdas

Query ExpressionsQuery Expressions

LINQLINQ

Partial MethodsPartial Methods

Local Variable Type InferenceLocal Variable Type Inference

private static void LocalVariableTypeInference(){

// Using the new 'var' keyword you can declare variables without having // to explicity declare their type. At compile time, the compiler determines // the type based on the assignment.int x = 10;var y = x;

// Since the type inference happens at compile time, you cannot declare // a 'var' without an assignment//var a;

// Output the type name for yConsole.WriteLine( y.GetType().ToString() );

}

Object InitializersObject Initializers

private static void ObjectInitializers(){

// Simplest way to create an object and set it's propertiesvar employee1 = new Employee();employee1.ID = 1;employee1.FirstName = "Bill";employee1.LastName = "Gates";Console.WriteLine( employee1.ToString() );

// We can always add a parameterized constructor to simplify codingvar employee2 = new Employee( 2, "Steve", "Balmer" );Console.WriteLine( employee2.ToString() );

// New way to create object, providing all the property value assignments// Works with any publicly accessible properties and fieldsvar employee3 = new Employee() { ID=3, FirstName="Clint", LastName="Edmonson" };Console.WriteLine( employee3.ToString() );

}

Collection InitializersCollection Initializers

private static void CollectionInitializers(){

// Create a prepopulated listvar employeeList = new List<Employee> {

new Employee { ID=1, FirstName="Bill", LastName="Gates" },new Employee { ID=2, FirstName="Steve", LastName="Balmer" },new Employee { ID=3, FirstName="Clint", LastName="Edmonson" }

};

// Loop through and display contents of listforeach( var employee in employeeList ){

Console.WriteLine( employee.ToString() );}

}

Anonymous TypesAnonymous Types

private static void AnonymousTypes(){

var a = new { Name = "A", Price = 3 };Console.WriteLine( a.GetType().ToString() );Console.WriteLine( "Name = {0} : Price = {1}", a.Name, a.Price );

}

Auto-Implemented PropertiesAuto-Implemented Properties

public class Employee{

public int ID{

get;set;

}

public string FirstName{

get;set;

}

public string LastName{

get;set;

}}

Extension MethodsExtension Methodspublic static class StringExtensionMethods{

// NOTE: When using an extension method to extend a type whose source // code you cannot change, you run the risk that a change in the implementation// of the type will cause your extension method to break.//// If you do implement extension methods for a given type, remember the following // two points:// - An extension method will never be called if it has the same signature // as a method defined in the type.// - Extension methods are brought into scope at the namespace level. For example,// if you have multiple static classes that contain extension methods in a single // namespace named Extensions, they will all be brought into scope by the using // Extensions; namespace.//public static int WordCount( this String str ){

return str.Split( new char[] { ' ', '.', '?' }, StringSplitOptions.RemoveEmptyEntries ).Length;

}}

// Usagestring s = "Hello Extension Methods";int i = s.WordCount();

Partial MethodsPartial Methods

// Employee.cspublic partial class Employee{

public bool Terminated{

get { return this.terminated; }set{

this.terminated = value;this.OnTerminated();

}}private bool terminated;

}

// Employee.Customization.cspublic partial class Employee{

// If this method is not implemented// compiler will ignore calls to itpartial void OnTerminated(){

// Clear the employee's ID numberthis.ID = 0;

}}

LINQ ExpressionsLINQ Expressionsprivate static void LinqExpressions(){

// Create a list of employeesvar employeeList = new List<Employee> {

new Employee { ID=1, FirstName="Bill", LastName="Gates" },new Employee { ID=2, FirstName="Steve", LastName="Balmer" },new Employee { ID=3, FirstName="Clint", LastName="Edmonson" }

};

// Search the list for founders using a lambda expressionvar foudersByLambda = employeeList.FindAll(

employee => (employee.ID == 1 || employee.ID == 2) );Console.WriteLine( foudersByLambda.Count.ToString() );

// Display collection using a lambda expressionfoudersByLambda.ForEach( employee => Console.WriteLine( employee.ToString() ) );

}

Query Expressions & Expression TreesQuery Expressions & Expression Treesprivate static void QueriesAndExpressions(){

// Create a list of employeesvar employeeList = new List<Employee> {

new Employee { ID=1, FirstName="Bill", LastName="Gates" },new Employee { ID=2, FirstName="Steve", LastName="Balmer" },new Employee { ID=3, FirstName="Clint", LastName="Edmonson" }

};

// Retrieve the founders via a LINQ queryvar query1 = from employee in employeeList

where employee.ID == 1 || employee.ID == 2 select employee;

var founders = query1.ToList<Employee>();founders.ForEach( founder => Console.WriteLine( founder.ToString() ) );

// Retrieve the new hires via a LINQ query that returns an anonymous typevar query2 = from employee in employeeList

where employee.ID == 3 select new {

employee.FirstName,employee.LastName

};var newHires = query2.ToList();newHires.ForEach( newHire => Console.WriteLine( newHire.ToString() ) );

}

Best PracticesBest Practices

Features are listed in increasing complexityFeatures are listed in increasing complexity

Don’t use features because they are new or Don’t use features because they are new or coolcool

Leverage new features to improve code Leverage new features to improve code readability and maintainabilityreadability and maintainability

Decide as a team to start using new features Decide as a team to start using new features and use them consistentlyand use them consistently

For More Information…For More Information…

Visual C# Developer CenterVisual C# Developer Centerhttp://msdn2.microsoft.com/en-us/vcsharp/default.aspxhttp://msdn2.microsoft.com/en-us/vcsharp/default.aspx

Accelerated C# 2008Accelerated C# 2008 by Trey Nash (Apress 2007) by Trey Nash (Apress 2007)

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