1. Tech·Ed North America 2009 5/18/2018 2:05 PM
© 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.

2. Getting the Most from Lambda Expressions
Tech·Ed  North America 2009
5/18/2018 2:05 PM
Getting the Most from Lambda Expressions
Deborah Kurata
President
InStep Technologies, Inc
Session Code: DTL315
© 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.

3. 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

4. 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:

5. You Are... Using Generic Lists Using Lambda Expressions
List(Of Customer)
List<Customer>
Using Lambda Expressions
Just getting started/new to them
Use them once in a while
Use them everyday

6. This Presentation is … Fun with Lambda Expressions
What are Lambda Expressions?
Lambdas as Generic Delegates
Lambdas as Callable Entities
Lambdas as Callbacks

7. Generic Lists Class Customer Class Customers Manages a single customer
Customer properties
Customer methods
Class Customers
Manages the list of customers
List(Of Customer)
List<Customer>

8. Fun With Lambda Expressions
5/18/2018 2:05 PM
demo
Fun With Lambda Expressions
© 2007 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.

9. Lambda Calculus
“Formal system designed to investigate function definition, function application, and recursion.”
Wikipedia

10. 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

11. 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

12. 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

13. Using Lambda Expressions
// C#
HelloButton.Click +=
(s, ev) =>
MessageBox.Show("Hello World");
' VB:
AddHandler HelloButton.Click, _
Function(s, ev) _
MessageBox.Show("Hello World")

14. Defining Delegates Named method Anonymous method (C# 2.0)
Lambda expression (C# 3.0 and VB 9)

15. 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) _

16. Lambda Expression Syntax – C#
' General syntax:
Customer foundCustomer =
allCust.First((Customer c) =>
c.CustomerId == 4);
' With inferred typing:
var foundCustomer =
allCust.First(c =>

17. Lambda Multiline Syntax – C#
var foundCustomer = allCust.First(c => {
Debug.WriteLine(c.FullName);
if (c.CustomerId == 4)
return true;
else
return false;
});

18. 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

19. Lambdas as Generic Delegates
Generic delegates were new in .NET 2.0
Predicate Delegates
Action Delegates
Func Delegates

20. 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

21. 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"));

22. demo Predicate Delegates 5/18/2018 2:05 PM
© 2007 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.

23. Action Delegate Encapsulates a method that does not return a value
Sub in VB
void in C#
Takes up to four parameters

24. Example: Action Delegate
' VB:
Can only use named methods
allCust.ForEach(AddressOf WriteToDebug)
// C#:
allCust.ForEach(c =>
Debug.WriteLine(c.FullName));

25. demo Action Delegates 5/18/2018 2:05 PM
© 2007 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.

26. 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)

27. Example: Func Delegate
' VB:
Dim total = allCust.Sum(Function(c) _
c.SalesTotal)
// C#:
var total = allCust.Sum(c =>
c.SalesTotal);

28. demo Func Delegates 5/18/2018 2:05 PM
© 2007 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.

29. Lambdas as Callable Entities
Lambda expressions can be assigned to a delegate variable
Lambda expression is executed when the delegate is executed

30. 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));

31. 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

32. Example: Local Variables
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))

33. demo Callable Entities 5/18/2018 2:05 PM
© 2007 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.

34. Lambdas as Callbacks Callback Passes a function to a function
“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

35. 5/18/2018 2:05 PM
demo
Callbacks
© 2007 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.

36. 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

37. Resources www.microsoft.com/teched www.microsoft.com/learning
Sessions On-Demand & Community
Microsoft Certification & Training Resources
Resources for IT Professionals
Resources for Developers
Microsoft Certification and Training Resources

38. 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

39. 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
Please visit us in the TLC blue area

40. Complete an evaluation on CommNet and enter to win!

41. 5/18/2018 2:05 PM
© 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.
© 2007 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.