The Singleton Module and Its Pattern In Ruby

Slide 1

Slide 1 text

The Singleton Module and Its Pattern In Ruby Ruby Conf 2019 : Nashville, TN : 11.19.2019

Slide 2

Slide 2 text

Hello! I’m Mike Calhoun You can find me at places on the internet where you would find people as @comike011 2

Slide 3

Slide 3 text

3 We’re Hiring!

Slide 4

Slide 4 text

Overview 2. Singleton.rb 3. Ruby Singleton Class 1. The Singleton Pattern 4

Slide 5

Slide 5 text

How Did We Get Here? Kismet or how curiosity got out of hand 5

Slide 6

Slide 6 text

Slide 7

Slide 7 text

Slide 8

Slide 8 text

Slide 9

Slide 9 text

“ The Singleton module implements the Singleton pattern 9

Slide 10

Slide 10 text

THANKS! Any questions? You can find me at @comike011 10

Slide 11

Slide 11 text

Overview 2. Singleton.rb 3. Ruby Singleton Class 1. The Singleton Pattern 11

Slide 12

Slide 12 text

1. The Singleton Pattern 12

Slide 13

Slide 13 text

What is The Singleton Pattern? ○ Restricts to a single instance 13

Slide 14

Slide 14 text

What is The Singleton Pattern? ○ Restricts to a single instance ○ Provides single access point to the resource 14

Slide 15

Slide 15 text

What is The Singleton Pattern? ○ Restricts to a single instance ○ Provides single access point to the resource ○ Not a global variable 15

Slide 16

Slide 16 text

What is The Singleton Pattern? ○ Restricts to a single instance ○ Provides single access point to the resource ○ Not a global variable ○ Problematic misuse 16

Slide 17

Slide 17 text

Are Singletons Bad? Bart Jacobs, January 16, 2018 17

Slide 18

Slide 18 text

“ I agree that the singleton pattern seems convenient and it may occasionally be warranted to use it, but the drawbacks far outweigh the benefits. 18

Slide 19

Slide 19 text

6 Reasons Why You Should Avoid Singletons David Tanzer, last accessed 9/18/2019 19

Slide 20

Slide 20 text

“ Yes, I am really writing a blog about why the “Singleton Pattern” is bad. In 2016. But it comes up in discussions time and again, so here is a list of reasons why you should avoid singletons. 20

Slide 21

Slide 21 text

Why The Singleton Pattern Sucks and You Should Avoid It WDIS, February 29, 2016 21

Slide 22

Slide 22 text

“ Most of these patterns [from GoF] are straightforward and frankly plain logical...However, there is one specific pattern that gets hate from every coding-related website on the Internet...the infamous Singleton Pattern, probably the most overused and frequently misplaced programming anti-pattern of all time 22

Slide 23

Slide 23 text

Why Singletons are Evil Scott Densmore, May 25, 2004 23

Slide 24

Slide 24 text

Singletons Are Pathological Liars Miško Hevery, April 17, 2008 24

Slide 25

Slide 25 text

Patterns I Hate: #1 Singletons Alex Miller, July 3, 2007 25

Slide 26

Slide 26 text

Singletons I Love You, But You’re Bringing Me Down codingwithoutcomments, October 4, 2008 26

Slide 27

Slide 27 text

Singletons Are Great and You Should Use Them 27

Slide 28

Slide 28 text

Singletons Are Great and You Should Use Them Citation Needed 28

Slide 29

Slide 29 text

Concerns ○ Concurrent access to a shared resource 29

Slide 30

Slide 30 text

Concerns ○ Concurrent access to a shared resource ○ Global state 30

Slide 31

Slide 31 text

Concerns ○ Concurrent access to a shared resource ○ Global state ○ Violation of SRP 31

Slide 32

Slide 32 text

Concerns ○ Concurrent access to a shared resource ○ Global state ○ Violation of SRP ○ Testing is problematic 32

Slide 33

Slide 33 text

Concerns ○ Concurrent access to a shared resource ○ Global state ○ Violation of SRP ○ Testing is problematic ○ Encourages tight coupling 33

Slide 34

Slide 34 text

Common Appropriate Use Cases ○ Unidirectional flow of data 34

Slide 35

Slide 35 text

Common Appropriate Use Cases ○ Unidirectional flow of data ○ Resource requested from multiple and disparate areas 35

Slide 36

Slide 36 text

Common Appropriate Use Cases ○ Unidirectional flow of data ○ Resource requested from multiple and disparate areas ○ Logging 36

Slide 37

Slide 37 text

Common Appropriate Use Cases ○ Unidirectional flow of data ○ Resource requested from multiple and disparate areas ○ Logging ○ Configurations 37

Slide 38

Slide 38 text

Common Appropriate Use Cases ○ Unidirectional flow of data ○ Resource requested from multiple and disparate areas ○ Logging ○ Configurations ○ Nothing modified within the application 38

Slide 39

Slide 39 text

Overview 2. Singleton.rb 3. Ruby Singleton Class 1. The Singleton Pattern 39

Slide 40

Slide 40 text

2. singleton.rb 40

Slide 41

Slide 41 text

singleton.rb ○ .new and .allocate are made private 41

Slide 42

Slide 42 text

singleton.rb ○ .new and .allocate are made private ○ .instance added 42

Slide 43

Slide 43 text

singleton.rb ○ .new and .allocate are made private ○ .instance added ○ .clone and .dup raise TypeError 43

Slide 44

Slide 44 text

Slide 45

Slide 45 text

Slide 46

Slide 46 text

Slide 47

Slide 47 text

Slide 48

Slide 48 text

Slide 49

Slide 49 text

Slide 50

Slide 50 text

Slide 51

Slide 51 text

Slide 52

Slide 52 text

Slide 53

Slide 53 text

Slide 54

Slide 54 text

Slide 55

Slide 55 text

Slide 56

Slide 56 text

Slide 57

Slide 57 text

Slide 58

Slide 58 text

Slide 59

Slide 59 text

Slide 60

Slide 60 text

Slide 61

Slide 61 text

Slide 62

Slide 62 text

Slide 63

Slide 63 text

Slide 64

Slide 64 text

Overview 2. Singleton.rb 3. Ruby Singleton Class 1. The Singleton Pattern 64

Slide 65

Slide 65 text

3. Ruby Singleton Class 65

Slide 66

Slide 66 text

Singleton class ○ Also referred to as ‘eigenclasses’ or ‘metaclasses’ 66

Slide 67

Slide 67 text

Singleton class ○ Also referred to as ‘eigenclasses’ or ‘metaclasses’ ○ Somewhat hidden 67

Slide 68

Slide 68 text

Singleton class ○ Also referred to as ‘eigenclasses’ or ‘metaclasses’ ○ Somewhat hidden ○ Essential to the Ruby Object Model 68

Slide 69

Slide 69 text

Slide 70

Slide 70 text

The Ruby Object Model ○ BasicObject, Object, 70

Slide 71

Slide 71 text

The Ruby Object Model ○ BasicObject, Object, ○ Modules are included above their including object 71

Slide 72

Slide 72 text

Slide 73

Slide 73 text

Slide 74

Slide 74 text

Slide 75

Slide 75 text

Slide 76

Slide 76 text

Slide 77

Slide 77 text

An Example What and where is the singleton class? 77

Slide 78

Slide 78 text

Slide 79

Slide 79 text

79 Porch Cat "PK"

Slide 80

Slide 80 text

80 Porch Cat "PK" Pearl

Slide 81

Slide 81 text

Slide 82

Slide 82 text

Slide 83

Slide 83 text

Slide 84

Slide 84 text

Slide 85

Slide 85 text

Slide 86

Slide 86 text

Slide 87

Slide 87 text

Slide 88

Slide 88 text

Slide 89

Slide 89 text

Slide 90

Slide 90 text

Slide 91

Slide 91 text

Slide 92

Slide 92 text

Slide 93

Slide 93 text

Slide 94

Slide 94 text

Slide 95

Slide 95 text

Slide 96

Slide 96 text

Slide 97

Slide 97 text

Slide 98

Slide 98 text

Slide 99

Slide 99 text

Slide 100

Slide 100 text

100

Slide 101

Slide 101 text

101

Slide 102

Slide 102 text

102

Slide 103

Slide 103 text

103

Slide 104

Slide 104 text

104

Slide 105

Slide 105 text

105

Slide 106

Slide 106 text

106

Slide 107

Slide 107 text

107

Slide 108

Slide 108 text

108

Slide 109

Slide 109 text

109

Slide 110

Slide 110 text

110

Slide 111

Slide 111 text

111

Slide 112

Slide 112 text

112

Slide 113

Slide 113 text

113

Slide 114

Slide 114 text

114

Slide 115

Slide 115 text

115

Slide 116

Slide 116 text

116

Slide 117

Slide 117 text

117

Slide 118

Slide 118 text

118

Slide 119

Slide 119 text

119

Slide 120

Slide 120 text

120

Slide 121

Slide 121 text

121

Slide 122

Slide 122 text

Overview 2. Singleton.rb 3. Ruby Singleton Class 1. The Singleton Pattern 122

Slide 123

Slide 123 text

123

Slide 124

Slide 124 text

THANKS! 124 Mike Calhoun (@comike011)