Rando

A lightning talk in which we learn a bit about Ruby by working with random values.

Transcript

1. Rando # Ruby v2.1.1 Random.srand 123 1
2. four random things 2
3. pick a random number between 100 and 200 3
4. (rand * 100 + 100).to_i => 169 4
5. (rand * 100 + 100).to_i => 169 NO! 5
6. rand(100..200) => 166 6
7. rand(*args) 7
8. how many kinds of random does Ruby have? 8
9. ObjectSpace .each_object .select { |obj| obj.respond_to?(:rand) } 9
10. Kernel Random #<Random:0x007fed39068820> 10
11. Kernel Random #<Random:0x007fed39068820> Random::DEFAULT => #<Random:0x007fed39068820> 11
12. Kernel Random #<Random:0x007fed39068820> 12
13. rand == Kernel.rand Random.rand == Random::DEFAULT.rand Kernel.rand != Random.rand 13
14. Kernel.rand => 0.6964691855978616 Random.rand => 0.6964691855978616 14
15. Kernel.rand(100) => 66 Random.rand(100) => 66 15
16. Kernel.rand(0..100) => 66 Random.rand(0..100) => 66 16
17. Kernel.rand(100.0) => 66 Random.rand(100.0) => 69.64691855978616 17
18. Kernel.rand(-100.0) => 66 Random.rand(-100.0) => ArgumentError 18
19. know your rand 19
20. generate a list of random numbers 20
21. (0..20).map { rand } => [0.696469, 0.286139, ...] 21
22. (0..20).map { rand } => [0.696469, 0.286139, ...] NO! 22
23. Array.new(20) { rand } => [0.696469, 0.286139, ...] 23
24. Array.new(*args) 24
25. Array.new(size, obj, &generator) 25
26. Array.new(3) => [nil, nil, nil] 26
27. Array.new(3, 0) => [0, 0, 0] 27
28. Array.new(3) { |n| n } => [0, 1, 2] 28
29. know your primitives 29
30. pick a random subset of elements from an array 30
31. users = %w[alice bob carol] subset = Array.new(2) { users[rand * users.length] } => ['bob', 'alice'] 31
32. users = %w[alice bob carol] subset = Array.new(2) { users[rand * users.length] } => ['bob', 'alice'] NO! 32
33. users = %w[alice bob carol] users.sample(2) => ['bob', 'carol'] 33
34. Array#sample(*args) 34
35. Array#sample(size, random: rng) 35
36. a = [1,2,3,4,5] a.sample => 3 36
37. a = [1,2,3,4,5] a.sample(3) => [3, 1, 5] 37
38. a = [1,2,3,4,5] a.sample(1) => [3] 38
39. a = [1,2,3,4,5] rng = Random.new(234) a.sample(random: rng) => 1 39
40. a = [1,2,3,4,5] rng = Random.new(234) a.sample(3, random: rng) => [1, 5, 2] 40
41. a = [1,2,3,4,5] rng = Random.new(234) a.shuffle(random: rng) => [3, 2, 5, 4, 1] 41
42. know your primitives (seriously) 42
43. generate a secure token from random values 43
44. token = '' 40.times do token << rand(0..255).to_s(16) end => 'fe6d7e42dc62e6115...' 44
45. token = '' 40.times do token << rand(0..255).to_s(16) end => 'fe6d7e42dc62e6115...' NO! 45
46. require 'securerandom' token = SecureRandom.hex(40) => '6011e8861f024cb75...' 46
47. require 'securerandom' token = SecureRandom.hex(40) => '6011e8861f024cb75...' => '8f90ea2187b50cb52...' => 'cad2eb20a39939601...' => '272a822296de5b249...' => 'ad65839e646c27252...' 47
48. know your security (seriously) 48
49. hopefully you didn't learn anything 49