1. Introduction to AOP
Dror Helper
@dhelper

2. About.Me
 Software developer and technical lead
 PostSharp MVP
 Blogger: http://blog.drorhelper.com

3. Developer write code
void transfer(Account fromAcc, Account toAcc, int amount)
{
if (fromAcc.getBalance() < amount)
{
throw new InsufficientFundsException();
}
fromAcc.withdraw(amount);
toAcc.deposit(amount);
}

4. Permission support – Right away!
void transfer(Account fromAcc, Account toAcc, int amount, User user)
{
if (! checkUserPermission(user))
{
throw new UnauthorizedUserException();
}
if (fromAcc.getBalance() < amount)
{
throw new InsufficientFundsException();
}
fromAcc.withdraw(amount);
toAcc.deposit(amount);
}

5. Need to check parameters – Done!
void transfer(Account fromAcc, Account toAcc, int amount, User user)
{
if(fromAcc == null || toAcc == null)
{
throw new IllegalArgumentException ();
}
if(balance <= 0)
{
throw new IllegalArgumentException ();
}
if (! checkUserPermission(user))
{
throw new UnauthorizedUserException();
}
if (fromAcc.getBalance() < amount)
{
throw new InsufficientFundsException();
}
fromAcc.withdraw(amount);
toAcc.deposit(amount);
}

6. Needs logging – no problems!
void transfer(Account fromAcc, Account toAcc, int amount, User user)
{
logger.info("transferring money...");
if(balance <= 0)
{
throw new IllegalArgumentException ();
}
if (! checkUserPermission(user))
{
logger.info("User has no permission.");
throw new UnauthorizedUserException();
}
if (fromAcc.getBalance() < amount)
{
logger.info("Insufficient Funds, sorry");
throw new InsufficientFundsException();
}
fromAcc.withdraw(amount);
toAcc.deposit(amount);

7. And finally – exception handling
void transfer(Account fromAcc, Account toAcc, int amount, User user)
{
logger.info("transferring money...");
if(balance <= 0)
{
throw new IllegalArgumentException ();
}
if (! checkUserPermission(user))
{
logger.info("User has no permission.");
throw new UnauthorizedUserException();
}
if (fromAcc.getBalance() < amount)
{
logger.info("Insufficient Funds, sorry");
throw new InsufficientFundsException();
}
try
{
fromAcc.withdraw(amount);
toAcc.deposit(amount);
}
catch(Exception exc)
{
logger.info(“failed transaction.");
return;
}

8. What can we do?

9. The Problem
 Code duplication
 Hard to read
 Difficult to maintain
 Not all programmers code the same
Ctrl + C, Ctrl + V

10. Problem - Cross cutting concerns
Customer Product Order
Logging
Cross-Cutting
Security
Concerns
Caching

11. Non-Functional Requirements
 Security
 Caching
 Tracing
 Exception handling
 Monitoring
 Validation
 Persistence
 Transactions
 Thread sync

12. Solution  AOP
 Separation of concerns
 Extension of OOP
1. Encapsulate Cross cutting concerns into aspects
2. Apply aspects to code

13. Why AOP
• AOP exist for more then 15
Mature years
Industry • Industry standard
adopted
Observed • -15% lines of code
Benefits • -20% decoupling

14. Terminology

15. Join Point
static void Main()
{
myClass1.Func1
var myClass1 = new MyClass();
var myClass2 = new MyClass();
myClass1.Func1();
myClass1.Func2(2, 3);
myClass1.Func2
myClass2.Func2(4, 5);
}
myClass2.Func2

16. Point Cuts
myClass1.Func1
myClass1.Func2 Before Func2
myClass2.Func2

17. Advice
 The code to run
 Typically small
 Injected at join point

18. Aspect
Join Point + Advice = Aspect

19. How to “do” AOP

20. Our example for today – the calculator

21. My co-worker solution

22. #1 Functional programming
 Using higher order functions to “warp” existing code
 Decorator pattern

23. 1# Functional Programming
+ -
 No additional  You cannot automatically
dependency in your pass context from the
caller to the aspect code
build or runtime code.
 Must modify the code of
 Programmers are every method to which
already familiar with the you want to add the
technology. aspect.
 Aspect composition is less
convenient.

24. Why not use existing tools

25. What IoC containers can do for you?
 Enable Dependency Injection (DI)
 Create objects and satisfy it’s dependencies
 A lot more..

26. #2 Dynamic proxies
Framework
Application Proxy Aspect Object

27. .NET IoC tools
 Unity http://unity.codeplex.com/
 Spring.NET http://www.springframework.net/
 Castle http://www.castleproject.org/

28. Dynamic proxies
+ -
 You may already be  Very limited aspect-oriented
features.
using a DI framework.
 Your objects must be
instantiated using the
 Aspects can be container
configured after build.
 Does not work on
static, non-public, and/or
 Some aspects may be non-virtual methods
provided by the
 Does not work on
framework. fields, properties, or events.

29. #3 MSIL transformations
IL Final
Code Compile
weaving Assembly

30. IL transformation tools
 Mono.Cecil http://www.mono-project.com/Cecil
 NotifyPropertyWeaver
http://code.google.com/p/notifypropertyweaver/

31. MSIL transformations
+ -
 Very powerful. You can  Requires an advanced
knowledge of MSIL.
achieve virtually any
code transformation  Very low level
 These frameworks are  typically do not compose
well when many are
free of charge and applied to the same
backed by large method.
companies.
 No Visual Studio tooling.

32. #4 Build time AOP
Build Process
Intermediate
Final
Source Compiler Assembly AOP Assembly
Code (IL)
Aspects

33. Summery
Use AOP because:
 Less code = fewer bugs
 Less code = easier to read and maintain
 Reduce duplicate code
 Improve team work/architecture
 Reduce development cost

34. Resources
Cross Cutting Concerns blog
http://crosscuttingconcerns.com/
My blog: http://blog.drorhelper.com