Types and Refactoring

A talk about types and refactoring I gave at Brighton Ruby 2014.

Transcript

1. Types & Refactoring
2. a!/samphippen
3. Types
4. I think type systems are great!
5. I think dynamic languages are great!
6. I think thinking about types in dynamic languages is great!
7. RUUUUUUUUUUUUUUUUUUUUUUUUU UUUUUUUUUUUUUUUUUUUUUUUUUU UUUUUUUUUUUUUUUUUUUUUUUUUU UUUUUUUUUUUUUUUUUUUUUUUUUU UUUUUUUUUUUUUBYYYYYYYYYYYYYY YYYYYYYYYYYYYYYYYYYYYYYYYYYYYY YYYYYYYYYYYYYYYYYYYYYYYYYYYYYY YYYYYYYYYYYYYYYYYYYYYYYYYYYYYY
8. No type systems here
9. NoMethodError: undefined method `foo' for nil:NilClass
10. No explicit type systems here
11. What is a type?
12. Concrete implementation of some data and behaviour
13. Class
14. 1.class # => FixNum
15. (1.0).class # => Float
16. What is a typeclass?
17. A set of methods satisfied by many types
18. Interface
19. (1+1.0).class # => Float (1.0+1).class # => Float
20. But also things like
21. Positive Int + Positive Int # => Positive Int
22. some_collection.count
23. String Hash Array
24. Form a typeclass (or interface) under count with no args
25. Methods that return consistent interfaces are great
26. The problem
27. We’re not forced to return a single interface
28. If interface is inconsistent, code must check types further down
29. For example returning nil
30. nil is not type classed the same as your object!
31. pony = Pony.find_by(:key => value) if pony pony.neigh else puts “pony was nil” end
32. The if is a subtle form of type checking.
33. Type checking is the antithesis of OO
34. Can we get a consistent interface?
35. Refactoring
36. Null object
37. class Pony def horse_power 0.5 end end
38. Pony.find_by( :key => value ) || NullPony.new
39. class NullPony def horse_power 0 end end
40. Decides default for horse_power at define time
41. May or may not be what you want
42. Maybe
43. Steal ideas from functional programming!
44. Decide defaults at run time
45. Maybe is a type class
46. #map(&blk) -> maybe #value_or(x) -> Object
47. class Just def initialize(value) @value = value end def map(&blk) def value_or(x) Just.new(blk.call(@value)) @value end end end
48. class Nothing def map(&blk) self end def value_or(x) x end end
49. Map until done with transforms
50. use maybe.value_or(“something”)
51. Recap
52. Methods that return nil are almost always inconsistently typed
53. Use a null object to replace a nil if you know defaults at define time
54. Use maybe if you want to set defaults at run time
55. RSpec RSpec ! ! RSpec 3
56. tinyurl.com/ sambr2014
57. Let’s have some questions a!/samphippen sam@funandplausible.com