Groovy with Style -- Groovy Grails eXchange 2014

What should "idiomatic" Groovy code look like? What are the good practices in terms of syntax style, typing preferences? What are the nice shortcuts to be aware of to be more productive? Guillaume Laforge will answer those questions along the way!

1. Guillaume Laforge 
 @glaforge with Style
2. Guillaume Laforge Groovy project lead @glaforge http://google.com/+GuillaumeLaforge http://glaforge.appspot.com
3. 11+ years of experience with Groovy
4. What style?
5. A touch of code style
6. A bit of puzzlers
7. Some glittering gems
8. And advice from the wise
12. <=>
13. @glaforge http://beta.groovy-lang.org/style-guide.html 10
14. @glaforge http://beta.groovy-lang.org/style-guide.html 10
17. I’ll have to run to King Cross Saint Pancras right after the talk!
20. @glaforge No semicolons! 14 class HelloLondon {
 private String message = 'Hello London';
 String greet(String name) {
 "$message, $name speaking";
 } 
 }
 
 print new HelloLondon().greet('Guillaume');
21. @glaforge No semicolons! 14 class HelloLondon {
 private String message = 'Hello London';
 String greet(String name) {
 "$message, $name speaking";
 } 
 }
 
 print new HelloLondon().greet('Guillaume');
22. @glaforge No semicolons! 15 class HelloLondon {
 private String message = 'Hello London'
 String greet(String name) {
 "$message, $name speaking"
 } 
 }
 
 print new HelloLondon().greet('Guillaume')
24. @glaforge Public by default 17 public class HelloLondon {
 private String message = 'Hello London'
 private String name
 
 public HelloLondon(String name) {
 this.name = name
 }
 public String greet() {
 return "$message, $name speaking"
 } 
 }
25. @glaforge Public by default 18 class HelloLondon {
 private String message = 'Hello London'
 private String name
 
 HelloLondon(String name) {
 this.name = name
 }
 String greet() {
 return "$message, $name speaking"
 } 
 } Methods and classes are public by default
26. @glaforge Fields and static fields require visibility 19 class HelloLondon {
 static String message = 'Hello London'
 String name
 
 HelloLondon(String name) {
 this.name = name
 }
 String greet() {
 return "$message, $name speaking"
 } 
 }
27. @glaforge Fields and static fields require visibility 19 class HelloLondon {
 static String message = 'Hello London'
 String name
 
 HelloLondon(String name) {
 this.name = name
 }
 String greet() {
 return "$message, $name speaking"
 } 
 } You created both an instance property and a static property!
28. Till ‘def’ do us part!
29. @glaforge Get rid of the useless ‘def’ 21 class HelloLondon {
 private String message = 'Hello London'
 private def String name
 def HelloLondon(def String name) {
 this.name = name
 }
 public def String greet() {
 def String result = "$message, $name speaking"
 return result
 } 
 }

30. @glaforge Get rid of the useless ‘def’ 21 class HelloLondon {
 private String message = 'Hello London'
 private def String name
 def HelloLondon(def String name) {
 this.name = name
 }
 public def String greet() {
 def String result = "$message, $name speaking"
 return result
 } 
 }

31. @glaforge Get rid of the useless ‘def’ 22 class HelloLondon {
 private String message = 'Hello London'
 private String name
 HelloLondon(String name) {
 this.name = name
 }
 String greet() {
 String result = "$message, $name speaking"
 return result
 } 
 }

32. @glaforge Get rid of the useless ‘def’ 23 class HelloLondon {
 private String message = 'Hello London'
 private String name
 HelloLondon(String name) {
 this.name = name
 }
 String greet() {
 def result = "$message, $name speaking"
 return result
 } 
 }
 But it’s fine to use ‘def’ for local variables
34. @glaforge Return is optional too 25 String greet() { 
 return "$message, $name speaking"
 }
35. @glaforge Return is optional too 25 String greet() { 
 return "$message, $name speaking"
 }
36. @glaforge Return is optional too 26 String greet() { 
 "$message, $name speaking"
 }
37. @glaforge Return is optional too 26 String greet() { 
 "$message, $name speaking"
 } But return is fine for early returns, or for clarity of intent
38. @glaforge Optional return for if / else 27 int color(String name) {
 if (name == 'red')
 1
 else if (name == 'green')
 2
 else
 -1
 }
39. @glaforge Optional return for switch / case 28 int color(String name) {
 switch (name) {
 case 'red': 1; break
 case 'green': 2; break
 default: -1
 }
 }
40. @glaforge Optional return for switch / case 28 int color(String name) {
 switch (name) {
 case 'red': 1; break
 case 'green': 2; break
 default: -1
 }
 } Yeah, yeah, ugly semicolon and break…
41. @glaforge Optional return for try / catch 29 boolean isInt(String s) {
 try {
 Integer.parseInt(s)
 true
 } catch (NumberFormatException nfe) {
 false
 } finally {
 println 'done'
 }
 }
 
 assert isInt('123') && assert !isInt('abc')
42. @glaforge Optional return for try / catch 29 boolean isInt(String s) {
 try {
 Integer.parseInt(s)
 true
 } catch (NumberFormatException nfe) {
 false
 } finally {
 println 'done'
 }
 }
 
 assert isInt('123') && assert !isInt('abc') ‘finally’ blocks don’t return a value
44. @glaforge Omit parentheses 31 println('Hello, World')
45. @glaforge Omit parentheses 32 println 'Hello, World'
46. @glaforge Command chains 33 move forward at 3.km/h
47. @glaforge Command chains 33 move forward at 3.km/h Parsed as: move(forward).at(3.getKm().div(h))
48. @glaforge Command chains and named arguments 34 check that: wine tastes good
49. @glaforge Command chains and named arguments 34 check that: wine tastes good Parsed as: check(that: wine).tastes(good)
50. @glaforge Trailing closure argument gets out 35 void unless(boolean b, Closure c) {
 if (!b) c()
 }
 
 def (speed, limit) = [80, 90]
 
 unless(speed > limit) {
 println "speed up a notch"
 }
51. @glaforge Trailing closure argument gets out 35 void unless(boolean b, Closure c) {
 if (!b) c()
 }
 
 def (speed, limit) = [80, 90]
 
 unless(speed > limit) {
 println "speed up a notch"
 } Parsed as: unless(speed > limit, {…})
53. @glaforge Class as first-class citizen 37 connection.doPost("${BASE_URI}/submit", params, ResourcesResponse.class)
54. @glaforge Class as first-class citizen 38 connection.doPost("${BASE_URI}/submit", params, ResourcesResponse)
56. @glaforge No need for dumb getters and setters 40 class Person {
 private String name
 private int age
 
 void setName(String name) {
 this.name = name
 }
 String getName() {
 this.name
 }
 void setAge(int age) {
 this.age = age
 }
 int getAge() {
 this.age
 }
 }
57. @glaforge No need for dumb getters and setters 41 class Person {
 String name
 int age
 }
58. @glaforge No need for dumb getters and setters 41 class Person {
 String name
 int age
 } Icing on the cake: add @Immutable or @Canonical
59. @glaforge Use the property notation 42 class Person {
 String name
 int age
 }
 
 def p = new Person(name: 'Guillaume', 
 age: 36)
 assert p.name == 'Guillaume'
 
 p.age = 37
 assert p.age == 37
61. @glaforge Use the named-argument constructor 44 
 
 
 
 
 def p = new Person(name: 'Guillaume', 
 age: 37)
 
 
 

62. @glaforge The @Builder transformation 45 import groovy.transform.builder.*
 
 @Builder
 class Person {
 String name
 int age
 }
 
 Person.builder() .name('Guillaume') .age(37) .build()
63. @glaforge The @Builder transformation 45 import groovy.transform.builder.*
 
 @Builder
 class Person {
 String name
 int age
 }
 
 Person.builder() .name('Guillaume') .age(37) .build() Different strategies available: chained setters, external builder class, type-safe initializer
65. @glaforge Equals and == 47 status != null && status.equals(Control.STATUS_COMPLETED)
66. @glaforge Equals and == 48 status == Control.STATUS_COMPLETED
68. @glaforge Use single quotes for String constants 50 def msg = 'Groovy Rocks!'
70. @glaforge Native syntax for data structures 52 def list = [1, 2, 3]
 def range = 'a'..'b'
 def map = [a: 1, b: 2, c: 3]
 def regex = ~/.*foo.*/
72. @glaforge The Groovy Development Kit 54
73. @glaforge The Groovy Development Kit 54
74. @glaforge The Groovy Development Kit 54 Know your GDK! So much groovy-ness in there!
76. @glaforge Switch / case on steroids 56 switch(obj) {
 case 123: "number 123"; break
 case "abc": "string abc"; break
 case String: "is a string"; break
 case [1, 2, 3]: "in list"; break
 case ~/.*o+.*/: "regex match"; break
 case { it < 3 }: "closure criteria"; break
 default: "unknown"
 }
78. @glaforge Import aliasing 58 import java.util.List as juList
 import java.awt.List as aList
 
 import javax.swing.WindowConstants as WC
79. @glaforge Import aliasing with static imports too 59 import static java.lang.Integer.parseInt as atoi
 
 assert atoi('123') == 123
81. @glaforge Groovy Truth 61 assert !( null )
 assert !( "" )
 assert !( [] )
 assert !( 0 ) assert new Object()
 assert "string"
 assert [1, 2, 3]
 assert 1234
82. @glaforge Groovy Truth 61 assert !( null )
 assert !( "" )
 assert !( [] )
 assert !( 0 ) assert new Object()
 assert "string"
 assert [1, 2, 3]
 assert 1234 False
83. @glaforge Groovy Truth 61 assert !( null )
 assert !( "" )
 assert !( [] )
 assert !( 0 ) assert new Object()
 assert "string"
 assert [1, 2, 3]
 assert 1234 False True
84. @glaforge Customize the truth with asBoolean() 62 class Account {
 String name
 boolean disabled = false
 
 boolean asBoolean() { !disabled }
 }
 
 assert new Account(name: 'current')
 assert !new Account(name: 'old', disabled: true)
87. @glaforge Safe navigation 64 // Java if (order != null) {
 if (order.getCustomer() != null) {
 if (order.getCustomer().getAddress() != null) {
 System.out.println(order.getCustomer().getAddress());
 }
 }
 }
 // Groovy println order?.customer?.address
88. @glaforge Safe navigation 64 // Java if (order != null) {
 if (order.getCustomer() != null) {
 if (order.getCustomer().getAddress() != null) {
 System.out.println(order.getCustomer().getAddress());
 }
 }
 }
 // Groovy println order?.customer?.address Also give more meaningful NPEs!
90. @glaforge Power Assert, coming from Spock 66 def (a, b, c, d) = [10, 20, 30, 610]
 assert a + b * c == d - 40
91. @glaforge Power Assert, coming from Spock 66 def (a, b, c, d) = [10, 20, 30, 610]
 assert a + b * c == d - 40 Assertion failed:
 
 assert a + b * c == d - 40
 | | | | | | | |
 10| 20| 30| | 570
 610 600 | 610
 false
93. @glaforge Calling Elvis for default values 68 def result = name != null ? name : "Unknown"
 
 def result = name ?: "Unknown"
94. @glaforge Calling Elvis for default values 68 def result = name != null ? name : "Unknown"
 
 def result = name ?: "Unknown" Groovy Truth 
 at play here
96. @glaforge Catch ‘any’ exception 70 try {
 something()
 } catch (any) {
 // ...
 }
97. @glaforge Catch ‘any’ exception 70 try {
 something()
 } catch (any) {
 // ...
 } Someone suggested me: catch(emAll)
99. @glaforge Of the importance of contracts • Use explicit typing for – method signatures – properties & fields • Nice for – Java interoperability – documenting your APIs – IDE auto-completion and refactoring 72
100. Thanks for your attention!
101. Q & A
102. @glaforge Picture credits Style: http://1hdwallpapers.com/wallpapers/my_style.jpg Eurostar: http://www.whatsupwhatson.com/wp-content/uploads/2014/04/Eurostar_3012_Waterloo.jpg Puzzle: http://joyinthecause.org/wp-content/uploads/2014/03/missing-puzzle-piece_00449088.jpg Gems: http://www.freewhd.com/blue-gems-wallpaper/ Wise: http://fc00.deviantart.net/fs70/i/2012/044/f/6/three_wise_men_color_by_csoro-d4pmlv2.jpg Ready: http://nameshapers.com/wp-content/uploads/2013/12/Social-Media-Coaching-for-CEOs-Getting-started.jpg Semicolon: http://www.freeimageslive.co.uk/image/view/3944/_original Till death to us part: https://mypencillines.files.wordpress.com/2013/04/img_0171.jpg Public: http://www.levelupliving.com/wp-content/uploads/2012/05/Fear-of-Public-Speaking-image.jpg Contract: https://www.icts.uiowa.edu/sites/default/files/contract.jpg Exception: http://www.quotescover.com/wp-content/uploads/Its-the-exception-that-proves__quotes-by-French-Proverb-77.png Banana: http://texturetaddka.com/wp-content/uploads/2011/10/DSC2008.jpg Elvis: http://natedsanders.com/blog/wp-content/uploads/2013/10/Elvis-Presley-Wallpaper-1280-x-960.jpeg Assert: http://www.itshouldjustworktm.com/wp-content/uploads/2012/03/assert-sign-photoshopped.jpg Compass: https://lh4.ggpht.com/WtY8QL0re9kMssF6q4RopDHC6QEpou7ybQo7qNRjn1X8Iu5uKUZv7huHA_PxPB8iGfs=h900 Safety vest: http://media.nautisports.com/catalog/product/image/gilet-de-sauvetage-gonflable-hydrostatique-hammar-pilot-275-n-avec-harnais-pro-rouge-nav_17452_web_1_1.jpg Class: http://upload.wikimedia.org/wikipedia/en/5/50/A_Class_in_Progress.jpg Aliasing: http://i.imgur.com/JrFly.png Light switch: http://www.hapihour.org/wp-content/uploads/2014/04/lighting-design-wall-light-winsome-designer-light-switches-australia-designer-light-switchesdesigner-light-switches-and-platesdesigner-light- switches-coversdesigner-light-switches-graydesign.jpg Steel structure: http://www.jingtabuilding.com/UploadFiles/sl6.jpg Quotes: http://g.fastcompany.net/multisite_files/fastcompany/poster/2013/09/3018353-poster-1280-quotess3.jpg Setter: http://upload.wikimedia.org/wikipedia/commons/b/b4/Rzesz%C3%B3w_Irish_Red_and_White_Setter_1pl.jpg Argument: http://www.familytreecounseling.com/kathysblog/wp-content/uploads/2014/01/arguing_couple.jpg Equal cupcake: http://static.communitytable.com/wp-content/uploads/2013/04/marriage-equality-cupcakes-ftr.jpg Obama truth: http://upload.wikimedia.org/wikipedia/commons/7/7c/Obama_swearing_in.JPG Quiz: http://a622.phobos.apple.com/us/r30/Purple/v4/df/a9/6e/dfa96e6c-ea9b-ee4c-4d6c-f9edf2775e1d/mzl.exfkkuro.png return: http://legacyofshadow.com/wp-content/uploads/2012/04/no-return-sign.jpg spock: http://trekcore.com/gallery/albums/spock09/spock_pb04.jpg London: http://www.100percentoptical.com/images/2014/10/london.jpg Tie fighter: http://img3.wikia.nocookie.net/__cb20090419001710/uncyclopedia/images/f/fe/Darthvader_tie_fighter.jpg 75