Rando

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