Transcript Deborah Kurata President InStep Technologies, Inc Session Code: DTL315 Deborah Kurata is... Consultant and President of: InStep Technologies, Inc. Author of: Doing Objects in VB 2005 Best Kept.

Deborah Kurata
President
InStep Technologies, Inc
Session Code: DTL315
Deborah Kurata is...
Consultant and President of:
InStep Technologies, Inc.
Author of:
Doing Objects in VB 2005
Best Kept Secrets in .NET
Software designer/developer
INETA Speaker
Microsoft MVP
[email protected]
InStep Technologies is...
Consulting
Mentoring services to get you started and keep you
going with .NET
Strategic software consulting and training services
Application architecture and design
Custom software development of Windows and
Web-based applications
Web site: www.insteptech.com
You Are...
Using Generic Lists
List(Of Customer)
List<Customer>
Using Lambda Expressions
Just getting started/new to them
Use them once in a while
Use them everyday
This Presentation is …
Fun with Lambda Expressions
What are Lambda Expressions?
Lambdas as Generic Delegates
Lambdas as Callable Entities
Lambdas as Callbacks
Generic Lists
Class Customer
Manages a single customer
Customer properties
Customer methods
Class Customers
Manages the list of customers
List(Of Customer)
List<Customer>
Fun With Lambda Expressions
Lambda Calculus
“Formal system designed to investigate
function definition, function application, and
recursion.”
Wikipedia
What are Lambda Expressions?
New in Visual Basic 9 and C# 3.0 (VS 2008)
Unnamed, inline functions
Single statement
Multiple statement (C# only; coming in VB 10)
Used wherever delegates are required
What is a Delegate?
An object that holds a reference to a method
with a particular parameter list and return type
Like object-oriented, type-safe function pointer
Make it possible to treat methods as entities
Assign to variables
Pass as parameters
Classic Delegate Example: Events
// Passes the method to the new delegate
HelloButton.Click +=
new EventHandler(HelloButton_Click);
' AddressOf assigns the address of the
' method to the delegate
AddHandler HelloButton.Click, _
AddressOf HelloButton_Click
Using Lambda Expressions
// C#
HelloButton.Click +=
(s, ev) =>
MessageBox.Show("Hello World");
' VB:
AddHandler HelloButton.Click, _
Function(s, ev) _
MessageBox.Show("Hello World")
Defining Delegates
Named method
Anonymous method (C# 2.0)
Lambda expression (C# 3.0 and VB 9)
Lambda Expression Syntax - VB
' General syntax:
Dim foundCustomer as Customer = _
allCust.First(Function(c as Customer) _
c.CustomerId = 4)
' With inferred typing:
Dim foundCustomer = _
allCust.First(Function(c) _
c.CustomerId = 4)
Lambda Expression Syntax – C#
' General syntax:
Customer foundCustomer =
allCust.First((Customer c) =>
c.CustomerId == 4);
' With inferred typing:
var foundCustomer =
allCust.First(c =>
c.CustomerId == 4);
Lambda Multiline Syntax – C#
var foundCustomer = allCust.First(c =>
{
Debug.WriteLine(c.FullName);
if (c.CustomerId == 4)
return true;
else
return false;
});
Features that Use Delegates
Event handlers
Enumerable class methods
Extension methods of IEnumerable(T)
Examples: Aggregate, All, Any, FirstOrDefault
LINQ methods
Used by LINQ
Examples: OrderBy, Where, GroupBy
Lambdas as Generic Delegates
Generic delegates were new in .NET 2.0
Predicate Delegates
Action Delegates
Func Delegates
Predicate Delegate
Predicate: “An operator or function which
returns a Boolean value” - Wikipedia
Encapsulates a method that evaluates to True or
False
Takes one parameter
Example: Predicate Delegate
' VB:
Dim foundCustomer = _
Array.Find(custArray, Function(c) _
c.LastName.StartsWith("K"))
// C#:
var foundCustomer =
Array.Find(custArray, c =>
c.LastName.StartsWith("K"));
Predicate Delegates
Action Delegate
Encapsulates a method that does not return a
value
Sub in VB
void in C#
Takes up to four parameters
Example: Action Delegate
' VB:
Can only use named methods
allCust.ForEach(AddressOf WriteToDebug)
// C#:
allCust.ForEach(c =>
Debug.WriteLine(c.FullName));
Action Delegates
Func Delegate
Encapsulates a method that returns a value
Takes up to 4 parameters and a return value
Last parameter is the return value
Func<int, int, string>
Func(Of Integer, Integer, String)
Example: Func Delegate
' VB:
Dim total = allCust.Sum(Function(c) _
c.SalesTotal)
// C#:
var total = allCust.Sum(c =>
c.SalesTotal);
Func Delegates
Lambdas as Callable Entities
Lambda expressions can be assigned to a
delegate variable
Lambda expression is executed when the
delegate is executed
Example: Assignment
' VB:
Infers the type
Dim f = _
Function(x as Integer) (x + x).ToString()
Debug.WriteLine(f(5))
Debug.WriteLine(f(10))
// C#:
Func<int,string> f =
x => (x + x).ToString();
Debug.WriteLine(f(5));
Debug.WriteLine(f(10));
Lambda Expression Execution
Lambda expressions are executed when they
are called, not when they are constructed
Local variables used in a lambda expression are
“captured” or “lifted”
Variable value used is the value at execution time
Variable lifetime extends to the lifetime of the
delegate
Example: Local Variables
// C#:
int y = 0;
Func<int,string> f =
x => (x + y).ToString();
y = 10;
Debug.WriteLine(f(5));
' VB:
Dim y As Integer = 0
Dim f As Func(Of Integer, String) = _
Function(x) (x + y).ToString()
y = 10
Debug.WriteLine(f(5))
Callable Entities
Lambdas as Callbacks
Callback
“Executable code that is passed as an argument to
other code”
Passes a function to a function
A delegate does not know or care about the
class of the method it is referencing
No need to reference the class that defined the
method
Callbacks
Getting the Most from Lambdas
Use Lambda expressions for
Writing inline functions
Calling LINQ methods
Calling extension methods that take a delegate
Creating callable functions
Performing callbacks
Resources
www.microsoft.com/teched
www.microsoft.com/learning
Sessions On-Demand & Community
Microsoft Certification & Training Resources
http://microsoft.com/technet
http://microsoft.com/msdn
Resources for IT Professionals
Resources for Developers
www.microsoft.com/learning
Microsoft Certification and Training Resources
Related Content
DTL336 Future Directions for Visual Basic
Presenter(s): Jonathan Aneja, Anders Hejlsberg
DTL402 How LINQ Works: A Deep Dive into the Microsoft Visual Basic and C#
Implementations
Presenter: Jonathan Aneja
Track Resources
Visit the DPR TLC for a chance to win a copy of Visual Studio Team Suite. Daily drawing
occurs every day in the TLC at 4:15pm. Stop by for a raffle ticket
http://www.microsoft.com/visualstudio
http://www.microsoft.com/visualstudio/en-us/products/teamsystem/default.mspx
Please visit us in the TLC blue area
Complete an
evaluation on
CommNet and
enter to win!
© 2009 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.