What you need to know about static typing

Transcript

1. What you need to know about static typing
2. Introduction Lucas Uyezu Programmer Mentor Mechanical keyboard addict enthusiast @coralton @lucasuyezu
4. We're hiring!
5. • 800k+ merchants in 175 countries • RoR 6.1.0.alpha • Majestic Monolith with satellite services • Hundreds of developers • 50+ deploys per day
6. Ruby 3
7. Ruby 3 • Coming on Xmas 2020. • Speed (Ruby 3x3) • Concurrency • Static analysis
8. Some terminology
9. Weak/Strong typing vs Dynamic/Static typing
10. Strong Typing
11. • Defined what a strong tyepd language is in 1974. • One of the SOLID principles is named after her.
12. Barbara Liskov "... whenever an object is passed from a calling function to a called function, its type must be compatible with the type declared in the called function." -- 1974
13. Strong Typing lucasuyezu@Lucass-MBP ~/s/g/l/r/src> irb irb(main):001:0> 1 + '1'
14. Strong Typing lucasuyezu@Lucass-MBP ~/s/g/l/r/src> irb irb(main):001:0> 1 + '1' TypeError: String can't be coerced into Fixnum from (irb):1:in `+' from (irb):1 from /usr/bin/irb:11:in `<main>' irb(main):002:0>
15. Weak Typing
16. Weak Typing > 1 + '1'
17. Weak Typing > 1 + '1' "11"
18. Weak Typing > [] + {}
19. Weak Typing > [] + {} "[object Object]"
20. Weak Typing > {} + []
21. Weak Typing > {} + [] 0
23. WAT
24. Static Typing
25. Static Typing fn add(a: usize, b: usize) -> usize { return a + b }
26. Static Typing lucasuyezu@Lucass-MBP ~/s/g/l/rubyconfbr2019> cargo build Compiling rubyconfbr2019 v0.1.0 (file:///Users/lucasuyezu/src/github.com/lucasuyezu/rubyconfbr2019) error[E0308]: mismatched types --> main.rs:6:27 | 6 | println!("{:?}", add(1, '1')); | ^^^ expected usize, found char error: aborting due to previous error For more information about this error, try `rustc --explain E0308`. error: Could not compile `rubyconfbr2019`. To learn more, run the command again with --verbose.
27. Dynamic Typing
28. Dynamic Typing def add(a, b) a + b end
29. Dynamic Typing def add(a, b) a + b end lucasuyezu@Lucass-MBP ~/s/g/l/rubyconfbr2019> ruby main.rb Traceback (most recent call last): 2: from main.rb:5:in `<main>' 1: from main.rb:2:in `add' main.rb:2:in `+': String can't be coerced into Integer (TypeError)
30. Type checking in Ruby 3
31. • Optional. You won't need to change your Ruby code to run on Ruby 3. • Level 1: No signatures. Reports possible bugs. • May report false positives. • Level 2: requires signatures. Verifies that code complies with signatures. • Steep. • Sorbet. • RDL.
32. • Ruby 3 will provide a standard type signature format. • The official format is still WIP.
33. .rbs
34. .rbs • Ruby type signatures: github.com/ruby/ruby- signature • library developers will be able to bundle .rbs definitions. • application developers will be able to write their own for the ones missing.
35. # -- example.rbs -- class Array[A] include Enumerable def []: (Integer) -> A? def each: { (A)->void } -> self ... end
36. Sorbet
37. Sorbet • Level 2 static & runtime typechecking (We do runtime in development only) • Scalable: 100k LoC/second. 100x faster than rubocop. • It leverages Language Server Protocol so you can put it in your IDE. • 6 month private beta @ Shopify.
38. Why
39. Why • It eliminates a whole class of errors. • It's been proved successful by other languages (TypeScript, mypy). • You have small wins by just turning it on.
40. Sorbet Why: Gradual | All errors silenced All errors reported | |---------------------|--------------|-------------|---------------|---------------------| | typed: ignore | typed: false | typed: true | typed: strict | typed: strong |
41. Sorbet Why: Dead code if Random.rand foo = 1 else foo = 2 end editor.rb:5: This code is unreachable https://srb.help/7006 5 | foo = 2 ^ Errors: 1
42. Sorbet Why: Typos begin data = JSON.parse(File.read(path)) rescue JSON::ParseError => e raise "Got invalid JSON: #{e}" end json.rb:6: Unable to resolve constant ParseError 6 | rescue JSON::ParseError => e ^^^^^^^^^^^^^^^^ shims/gems/json.rbi:319: Did you mean: ::JSON::ParserError? 319 |class JSON::ParserError < JSON::JSONError ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
43. Example
44. Example def append_search_id(url, sid) return nil if url.nil? url + "?_sid=#{sid}" end
45. Example sig do params( url: T.nilable(String), sid: String ).returns(T.nilable(String)) end def append_search_id(url, sid) return nil if url.nil? url + "?_sid=#{sid}" end
46. Real world tips to go beyond type annotations
47. Pro tip Code smell Anti-pattern
48. Gradual
49. • Do not stop the world to add type annotations. • Keep delivering value and add them as you touch files. • Add a CI step, and runtime checks on development.
50. Primitive Obsession
51. Primitive Obsession The use of primitives like Strings and/or numbers for objects that need special handling. Aka Missing abstraction. Remember with_indifferent_access?
52. Example sig do params( url: T.nilable(String), sid: String ).returns(T.nilable(String)) end def append_search_id(url, sid) return nil if url.nil? url + "?_sid=#{sid}" end
53. Bug: URL with pre- existing params
54. Example sig do params( url: T.nilable(String), sid: String ).returns(T.nilable(String)) end def append_search_id(url, sid) return nil if url.nil? separator = url =~ /\?/ ? '&' : '?' url + "#{url}#{separator}_sid=#{sid}" end
55. Bug: search id is not escaped
57. sig do params( url: T.nilable(String), sid: String ).returns(T.nilable(String)) end def append_search_id(url, sid) return nil if url.nil? separator = url =~ /\?/ ? '?' : '&' sid = URI.encode(sid) url + "#{url}#{separator}_sid=#{sid}" end
58. Bug: URL already has sid param
60. Solution
61. Use an URI object sig do params( url: T.nilable(String), sid: String ).returns(T.nilable(String)) end def append_search_id(url, sid) return nil if url.nil? url = Addressable::URI.parse(url) params = url.query_values || {} params['_sid'] = sid url.query_values = params url.to_s end
62. Recieve and return an URI object sig do params( url: T.nilable(Addressable::URI), sid: String ).returns(T.nilable(Addressable::URI)) end def append_search_id(url, sid) return nil if url.nil? url = Addressable::URI.parse(url) params = url.query_values || {} params['_sid'] = sid url.query_values = params url end
63. Things that should not be primitives • URIs • IPs • Currency • Temperature • Measurements • Protip: (De)serialize them at the border.
64. Null Object
65. • Developed Quicksort in 1959/1960 • Inspiration for the occam language • Created the null reference
66. Sir Tony Hoare "I call it my billion-dollar mistake. It was the invention of the null reference in 1965. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years." -- QCon London, 2009
67. The case against null • Null references explode when they are used, not when they are returned. • It litters your code with null checks everywhere, disguised as .to_s, .to_i, .to_f, etc. • Modern languages like Rust don't have null by design. • C# introduced Nullable Reference Types, a stricter way of dealing with nulls.
68. Example
69. sig do params( url: T.nilable(Addressable::URI), sid: String ).returns(T.nilable(Addressable::URI)) end def append_search_id(url, sid) return nil if url.nil? url = Addressable::URI.parse(url) params = url.query_values || {} params['_sid'] = sid url.query_values = params url end
70. # restaurant_suggestions.rb class RestaurantSuggestion DEFAULT_IMAGE_URL_STRING = "https://example.com/no_image.png" attr_accessor :url_string end url = append_search_id(restaurant_suggestion.url_string, search_id)
71. # restaurant_suggestions.rb class RestaurantSuggestion DEFAULT_IMAGE_URL_STRING = "https://example.com/no_image.png" attr_accessor :url_string def url Addressable::URI.parse(url_string || DEFAULT_IMAGE_URL_STRING) end end ... url = append_search_id(restaurant_suggestion.url, search_id)
72. Example sig do params( url: Addressable::URI, sid: String ).returns(Addressable::URI) end def append_search_id(url, sid) params = url.query_values || {} params['_sid'] = sid url.query_values = params url end
73. Result
74. Result: Before def append_search_id(url, sid) return nil if url.nil? url + "?_sid=#{sid}" end
75. Result: After sig do params( uri: Addressable::URI, sid: String ).returns(Addressable::URI) end def append_search_id(uri, sid) params = uri.query_values || {} params[:_sid] = sid uri.query_values = params uri end
76. Takeaways
77. • Static type checkers and type annotations can help you find implicit concepts and code smells in your code. • Making these concepts explicit and fixing these smells is more important than adding type annotations.
78. Stuff like this: sig do returns(T::Array[T::Hash[T.any(String, Symbol), Object]]) end
79. • Avoid null references whenever possible. • Avoid primitives whenever possible. • Do not stop the world to implement sorbet. The key point is gradual typing. Add a CI step and move on.
80. Thank you!
81. Homework • EuRuKo 2019 - A Plan towards Ruby 3 Types by Yusuke Endoh • Sorbet Homepage • Strange Loop 2018 Stripe's Sorbet Talk • Null Object Design Pattern • Primitive Obsession Anti-pattern • WAT