Introduction to

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

2. Server-side Developer @

3. 600K+ DAU 150M reqs/day 15K IO op/s 200+ servers 40K+ concurrent users 2500 reqs/s 75ms avg latency

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

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

11. AOP AOP AOP AOP AOP AOP AOP

12. AOP

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

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. IoCframesworks • Castle • Spring.Net • Dynamic interceptors

29. Dynamic Proxies

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

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

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