The document discusses Ruby object-oriented programming (OOP) concepts. It explains that in Ruby, objects are more fundamental than classes. Classes are containers for object behavior that new objects can inherit from, but classes themselves are also objects. The document advocates thinking of objects first rather than being limited by classes and hierarchies, and discusses how this object-focused approach impacts concepts like singleton methods, private access, duck typing, and metaprogramming.

1. Ruby OOP: Objects over Classes
Aman King
king@thoughtworks.com
RubyConf India 2010

2. What is OOP?

3. What is a class?

4. What is an object?

5. But before the serious stuff …

6. Detouring through a comic book universe …
Image copyrighted by respective owners
Source: http://www.comics.org/

7. Coming back …

8. What is an object?

9. Something that takes birth …

10. exhibits some behavior …

11. interacts with other objects …

12. and finally dies off
or
is simply forgotten …

13. all in an effort to solve a problem.

14. What is a class?

15. A container for related behavior …

16. that a new object can start off with.

17. A class itself is an object …

18. used to create other objects.

19. When creating a new object,
a class calls the object’s
private initialize method.

20. Typically a class is named …

21. referenced via
a global constant variable.

22. A class object can have singleton
methods added to it.

23. These singleton methods can be
invoked wherever the class object
is accessible …

24. aka
“class-level methods”.

25. Why use classes?

26. Some possible reasons

27. An object remembers the class
used to create it …

28. explicit type checking
using kind_of? …

29. implicit type checking
using case syntax …

30. implicit type checking
using rescue syntax.

31. A class can build on other classes:
inheritance.

32. A class can share state
across multiple objects:
@@class_variables.

33. Some good reasons

34. A named container of behavior can
have more behavior added to it.

35. Any added behavior becomes part
of all objects created by that class.

36. A class can represent
a common pattern of initialization.

37. Classes improve
readability and maintainability.

38. What a class is not?

39. The fundamental building block
of an application.

40. A strong data type.

41. An enforcement of
contract or limitations
on how objects can behave.

42. Ruby’s object focus

43. Classes are objects.

44. No static method-lookup tables:
chain of ancestors.

45. Singleton methods.

46. Private access modifier
is object-level.

47. Duck typing.

48. Finding hints in the real world …

49. Objects over classes:
Consequences

50. Classes and hierarchies
no longer limit you.

51. Think through the usage of
class-level methods and variables:
globals?

52. Understanding meta-programming
is easier.

53. Effective and confident
use of meta-programming.

54. Final words

55. Objects are first-class citizens.

56. Classes are useful but secondary.

57. Thank you
king@thoughtworks.com
http://www.wikyblog.com/AmanKing