Introduction to AOP talk at DDD SouthWest 4.0, including examples of AOP using dynamic proxies, functional programming, dynamic language and PostSharp.

1. Introduction to
Aspect Oriented Programming
by Yan Cui @theburningmonk
theburningmonk.com

2. Server-side Developer @

4. • Overview
 Cross-Cutting Concerns
 AOP
 What’s in it for you
• AOP
 Terminologies
 AOP and OOP
 Solutions
• Q&A

5. the PROBLEM...
CROSS-CUTTING CONCERNS

6. Cross-Cutting Concerns
Image by Mike Rohde

7. • Cuts across multiple abstractions
• Difficult to decompose
• High-coupling
• Boilerplate code

8. • Code tangling and scattering
 Poor traceability
 Lower productivity
 Less code reuse
 Harder refactoring

9. the SOLUTION...
ASPECT-ORIENTED PROGRAMMING

10. “AOP is a programming paradigm which
aims to increase modularity by allowing
the separation of cross-cutting concerns”
- wikipedia

12. AOP
Image by Mike Rohde

14. • Centralize concerns implementation
• Intercept method calls
• Inject new behaviour
• More reusable code
• Cleaner code

15. What’s in it for YOU?

16. • Write less code
• Read less code
• More concise and easy to understand
• More maintainable

17. • Fewer code = FEWER DEFECTS!
• Less boilerplate code
• More interesting work
• Increased attention
• More PRODUCTIVITY!

18. dive a little deeper into...
AOP

19. • Join Point
 Place where behaviour can be added
 start/end of method
 property getter/setter
 ...

20. • Advice
 Code that’s injected at join points
 Logging
 Validation
 ...

21. • Point cut
 Join points where advice should be
applied

22. • Aspect
 Container holding point cuts and advice
 Aspect is to AOP what class is to OOP

23. • Weaving
 Combines advices with point cuts

24. • AOP is complementary to OOP
• AOP targets a specific problem
• Code modularization
 OOP – Real world objects
 AOP – Functionalities

25. • Help you S.O.L.I.Dify your code
 Single responsibility
 Open/close

26. • You can do AOP via:
 Dynamic Proxies
 Functional Programming
 Code Generation
 Dynamic Languages
 Static Weaving

27. AOP via...
DYNAMIC PROXIES

28. • IoC framesworks
 Castle
 Spring.Net
• Dynamic interceptors

29. Dynamic Proxies
Image by Mike Rohde

31. • Advantages
 Can use existing DI framework
 Built-in aspects (logging, etc.)
 Aspects can be configured after build

32. • Disadvantages
 Significant change to base code required to adapt
 Limited AOP features
 Do not work on static, non-public methods
 Do not work on fields, properties, or events
 Higher run-time overhead
 No build-time verification
 Objects must be instantiated using the container

33. NOOOO Sir!!
Class, is AOP the same as
Dependency Injection?

34. AOP via...
FUNCTIONAL PROGRAMMING

35. Functional
Programming
Image by Mike Rohde

37. • Advantages
 No external dependencies

38. • Disadvantages
 Requires modification to every function
 No support for matching rules
 Manual aspect composition

39. AOP via...
CODE GENERATION

40. • T4, CodeSmith tools

41. • Advantages
 Easy to generate complex source code

42. • Disadvantages
 Input is usually XML
 Cannot inject new behaviour to existing
code

43. AOP via...
DYNAMIC LANGUAGES

44. Dynamic Languages
Image by Mike Rohde

45. • Advantages
 Meta-programming is easy

46. • Disadvantages
 Switch to a dynamic language can be hard
 No (limited) Visual Studio tooling

47. AOP via...
STATIC WEAVING

48. • PostSharp, AspectJ
• Uses low-level MSIL transformation
• Compile time

49. Requirements
Aspect Decomposition
Aspects Core program
Aspect Recomposition
Final System

50. PostSharp
Image by Mike Rohde

51. • Advantages
 Most complete support of AOP features
 Aspect usage is verified at build time
 Better runtime performance

52. • Disadvantages
 Increased build time
 New to many developers

53. PostSharp Examples
• Auto-implement INotifyPropertyChanged
• Undo/Redo
• Thread dispatching
• Transaction handling
• Performance Monitoring

54. • Performance Monitoring
 Method execution time
 Method execution count
 Error count

55. Record exec time
Publish to Amazon CloudWatch

57. • Amazon CloudWatch
 Cheap to run
 Supports alarms and notifications
 Visualization tool

58. • http://bit.ly/KRDdgr

59. Thank You!
@theburningmonk
theburningmonk.com