fun Talk(): Exploring Kotlin Functions

Transcript

1. fun() Talk
   Exploring Kotlin Functions
   @n8ebel
   

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2. ♥
   == Kotlin + Functions
   @n8ebel #androidsummit 2
   

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3. ♥
   == Kotlin + Functions
   4 Free functions
   4 Higher-order functions
   4 Rich stdlib
   @n8ebel #androidsummit 3
   

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4. ♥
   == Kotlin + Functions
   4 arrayOf(), listOf()
   4 measureTimeMillis { doSomething() }
   4 orEmpty()
   4 forEach(), groupBy()
   @n8ebel #androidsummit 4
   

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5. Let's Have Some fun()
   Functions in Kotlin:
   - Easy to get started
   - Flexible & Convenient
   - Enable Freedom to Reimagine
   @n8ebel #androidsummit 5
   

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6. Easy to Get Started
   @n8ebel #androidsummit 6
   

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7. Easy to Get Started
   4 Can use the IDE conversion tool
   4 Can try online (https://try.kotlinlang.org)
   4 Easy to transfer existing knowledge
   @n8ebel #androidsummit 7
   

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8. From Java to Kotlin
   @n8ebel #androidsummit 8
   

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9. Hello Java Method
   class Greeter {
   void helloFunctions() {
   System.out.println("Yay, Functions");
   }
   }
   4 return type, name, method body
   @n8ebel #androidsummit 9
   

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10. Java Method Converted to Kotlin
    class Greeter {
    fun helloFunctions() {
    println("Yay, Functions")
    }
    }
    4 adds the fun keyword
    4 no explicit return type
    @n8ebel #androidsummit 10
    

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11. Further Simplification
    class Greeter {
    fun helloFunctions() = println("Yay, Functions")
    }
    @n8ebel #androidsummit 11
    

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12. Further Simplification
    fun helloFunctions() = println("Yay, Functions")
    @n8ebel #androidsummit 12
    

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13. Flexible & Convenient
    @n8ebel #androidsummit 13
    

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14. Flexible & Convenient
    4 Parameter & type flexibility
    4 Variations in scoping
    4 Variety of modifiers
    @n8ebel #androidsummit 14
    

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15. Parameter & Type Freedom
    4 Default parameters
    4 Named arguments
    4 Variable arguments
    4 Inferred return types
    4 Generic functions
    @n8ebel #androidsummit 15
    

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16. Parameter Basics
    @n8ebel #androidsummit 16
    

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17. Parameter Basics
    fun helloFunctions(excitingThing:String) {
    println("Yay, " + excitingThing)
    }
    helloFunctions("functions")
    // outputs "Yay, functions"
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18. Parameter Basics
    fun helloFunctions(exclamation:String, excitingThing:String) {
    println(exclamation + ", " + excitingThing)
    }
    helloFunctions("Yay", "functions")
    // outputs "Yay, functions"
    @n8ebel #androidsummit 18
    

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19. Default Parameters
    @n8ebel #androidsummit 19
    

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20. Default Parameters
    fun helloFunctions(exclamation:String, excitingThing:String = "functions") {
    println(exclamation + ", " + excitingThing)
    }
    // outputs "Yay, functions"
    helloFunctions("Yay", "functions")
    // outputs "Yay, functions"
    helloFunctions("Yay")
    @n8ebel #androidsummit 20
    

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21. Default Parameters
    4 function parameters can have default values
    4 when an argument is omitted, the default value is
    used
    @n8ebel #androidsummit 21
    

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22. Default Parameters
    4 allows us the flexibility of overloads without the
    verbosity of writing them
    4 help document the function contract by indicating
    what "sensible defaults" might be
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23. Default Parameters & Java
    4 Java doesn't have default parameter values
    4 must specify all parameter values when calling from
    Java
    @n8ebel #androidsummit 23
    

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24. Default Parameters & Java
    public class Main {
    // compiles
    GreetingFunctionsKt.helloFunctions("Yay", "functions");
    // does not compile
    GreetingFunctionsKt.helloFunctions("Yay");
    }
    @n8ebel #androidsummit 24
    

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25. Default Parameters & Java
    4 can use @JvmOverloads to generate overloads for
    each parameter
    4 generated overloads will use the specified default
    values
    @n8ebel #androidsummit 25
    

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26. Default Parameters & @JvmOverloads
    @JvmOverloads
    fun helloFunctions(exclamation:String, excitingThing:String = "functions") {
    println(exclamation + ", " + excitingThing)
    }
    @n8ebel #androidsummit 26
    

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27. @n8ebel #androidsummit 27
    

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28. Default Parameters & @JvmOverloads
    With the generated Java methods now available, both
    Java invocations now compile
    public class Main {
    GreetingFunctionsKt.helloFunctions("Yay", "functions");
    GreetingFunctionsKt.helloFunctions("Yay");
    }
    @n8ebel #androidsummit 28
    

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29. Named Arguments
    @n8ebel #androidsummit 29
    

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30. Named Arguments
    helloFunctions("functions", "functions")
    4 How do we know which value is correct?
    @n8ebel #androidsummit 30
    

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31. Named Arguments
    helloFunctions(exclamation = "yay!", excitingThing = "functions")
    4 Much easier to understand with named arguments
    @n8ebel #androidsummit 31
    

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32. Named Arguments
    4 Improve readability of function invocations
    4 Modify order of passed parameters by using named
    arguments
    4 Refactor parameter count/order without breaking
    code
    @n8ebel #androidsummit 32
    

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33. Named Arguments
    fun helloFunctions(exclamation:String, excitingThing:String = "functions") {
    println(exclamation + ", " + excitingThing)
    }
    helloFunctions("Hooray", "functions")
    helloFunctions("Hooray")
    helloFunctions(excitingThing = "functions", exclamation = "Hooray")
    // all output "Hooray, functions"
    @n8ebel #androidsummit 33
    

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34. Named Argument Limitations
    4 there are limitations to how named & positioned
    arguments are used
    4 once an argument name is specified, all subsequent
    arguments must be named as well
    @n8ebel #androidsummit 34
    

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35. Named Argument Limitations
    helloFunctions("hooray", "Android Summit")
    helloFunctions("hooray", excitingThing = "Android Summit")
    // both output "hooray, Android Summit"
    helloFunctions(excitingThing = "Android Summit", "hooray")
    // error: Mixing named and positioned arguments not allowed
    @n8ebel #androidsummit 35
    

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36. Named Arguments & Java
    4 Named arguments are not supported from Java
    4 Arguments must be passed in the order they are
    defined
    @n8ebel #androidsummit 36
    

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37. Variable Arguments
    @n8ebel #androidsummit 37
    

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38. Variable Number of Arguments
    We can define a parameter to accept a variable number
    of arguments T
    - use the vararg keyword
    - vararg param is then treated as an array of type T
    - default value must now be an array
    @n8ebel #androidsummit 38
    

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39. Variable Number of Arguments
    fun helloFunctions(exclamation:String, vararg excitingThings:String) {
    for(excitingThing in excitingThings) {
    println(exclamation + ", " + excitingThing)
    }
    }
    helloFunctions("yay!", "Android Summit", "Kotlin", "Android")
    // outputs:
    // yay!, Android Summit
    // yay!, Kotlin
    // yay!, Android
    @n8ebel #androidsummit 39
    

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40. Variable Number of Arguments
    Typically, a vararg parameter will be the last one
    Can be used in any order if:
    - other params are called using named argument syntax
    - last param is a function passed outside the
    parentheses
    @n8ebel #androidsummit 40
    

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41. Variable Number of Arguments
    This works
    helloFunctions("yay!", "Android Summit", "Kotlin", "Android")
    helloFunctions("Android Summit", "Kotlin", "Android", exclamation = "yay!")
    // both output:
    // yay!, Android Summit
    // yay!, Kotlin
    // yay!, Android
    @n8ebel #androidsummit 41
    

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42. Variable Number of Arguments
    This works
    helloFunctions("Android Summit", "Kotlin", "Android")
    // output:
    // "Android Summit, Kotlin"
    // "Android Summit, Android"
    @n8ebel #androidsummit 42
    

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43. Variable Number of Arguments
    This won't compile
    helloFunctions("Android Summit", exclamation = "yay!", "Kotlin", "Android")
    // error: "no matching function"
    @n8ebel #androidsummit 43
    

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44. Variable Number of Arguments
    Use "spread" operator to pass an existing array of
    values
    val thingsToBeExcitedAbout = arrayOf("Android Summit", "Kotlin", "Android")
    helloFunctions("yay!", *thingsToBeExcitedAbout)
    // output:
    // yay!, Android Summit
    // yay!, Kotlin
    // yay!, Android
    @n8ebel #androidsummit 44
    

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45. Variable Number of Arguments
    helloFunctions("yay!", "coffee", *thingsToBeExcitedAbout)
    helloFunctions("yay!", *thingsToBeExcitedAbout, "coffee")
    4 "Spreading" can be used alone, or with other passed
    varargs as well
    4 input array to the vararg parameter is handled in
    order
    @n8ebel #androidsummit 45
    

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46. Return Types
    @n8ebel #androidsummit 46
    

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47. Return Types
    What is the return type?
    fun helloFunctions(exclamation:String, excitingThing:String="functions") {
    println(exclamation + ", " + excitingThing)
    }
    4 If a function does not return any useful value, i
    ts
    return type is Unit
    @n8ebel #androidsummit 47
    

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48. Return Types
    These are equivalent
    fun helloFunctions(exclamation:String, excitingThing:String="functions") : Unit {
    println(exclamation + ", " + excitingThing)
    }
    fun helloFunctions(exclamation:String, excitingThing:String="functions") {
    println(exclamation + ", " + excitingThing)
    }
    @n8ebel #androidsummit 48
    

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49. Return Types: Non-Unit Type
    Functions with a block body require explicit return type
    & call for non-Unit functions
    fun helloFunctions(exclamation:String, excitingThing:String="functions") : String {
    return exclamation + ", " + excitingThing
    }
    @n8ebel #androidsummit 49
    

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50. Return Types: Non-Unit Type
    Can infer return type for single-expression functions
    fun helloFunctions(exclamation:String, excitingThing:String="functions")
    = exclamation + ", " + excitingThing
    @n8ebel #androidsummit 50
    

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51. Generic Functions
    @n8ebel #androidsummit 51
    

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52. Generic Functions
    4 Like classes, functions may have generic type
    parameters
    4 many stdlib functions are built with generics
    @n8ebel #androidsummit 52
    

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53. @n8ebel #androidsummit 53
    

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54. Variations In Scope
    @n8ebel #androidsummit 54
    

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55. Variations In Scope
    4 Top-level
    4 Member functions
    4 Local
    4 CompanionObject
    4 Extension functions
    @n8ebel #androidsummit 55
    

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56. Top-Level functions
    @n8ebel #androidsummit 56
    

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57. Top-Level functions
    4 Not associated with a class or object
    4 Defined within a Kotlin file
    4 Belong to their declared file's package
    4 Import to use within other packages
    @n8ebel #androidsummit 57
    

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58. Top-Level Function Patterns
    4 Replace stateless classes filled with static methods
    4 Swap your "Util" or "Helper" classes with functions
    @n8ebel #androidsummit 58
    

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59. Top-Level Function Considerations
    4 Not truly removing classes
    4 Generated as a public static method on a class using
    a special convention
    4 Kt.java
    @n8ebel #androidsummit 59
    

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60. Top-Level Function Considerations
    // inside Logging.kt
    package logging
    fun log(error:Throwable) {...}
    @n8ebel #androidsummit 60
    

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61. Top-Level Function Considerations
    Generated Code
    public class LoggingKt {
    public static void log(Throwable error) {...}
    }
    @n8ebel #androidsummit 61
    

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62. Top-Level Function Considerations
    // call from Kotlin
    log(Throwable("oops"))
    // call from Java
    LoggingKt.log(new Throwable("oops"))
    @n8ebel #androidsummit 62
    

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63. Top-Level Function Considerations
    Can override the generated class/file name
    4 Add @file:JvmName() to
    function's file
    4 Must be before the declared package
    @n8ebel #androidsummit 63
    

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64. Top-Level Function Considerations
    // inside Logging.kt
    @file:JvmName("LoggingFunctions")
    package logging
    fun log(error:Throwable) {...}
    @n8ebel #androidsummit 64
    

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65. Top-Level Function Considerations
    // call from Kotlin
    log(Throwable("oops"))
    // call from Java
    LoggingFunctions.log(new Throwable("oops"))
    @n8ebel #androidsummit 65
    

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66. Member Functions
    @n8ebel #androidsummit 66
    

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67. Member Functions
    4 Function associated with a class or object
    4 Have access to private members of the class or object
    @n8ebel #androidsummit 67
    

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68. Member Functions
    class Speaker() {
    fun giveTalk() { ... }
    }
    // create instance of class Speaker and call giveTalk()
    Speaker().giveTalk()
    @n8ebel #androidsummit 68
    

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69. Member Function Considerations
    4 Default arguments can't be changed in overridden
    methods
    4 If overriding a method, you must omit the default
    values
    @n8ebel #androidsummit 69
    

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70. Local Functions
    @n8ebel #androidsummit 70
    

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71. Local Functions
    Functions inside of functions
    4 Create a function that is scoped to another function
    4 Useful if your function is only ever called from
    another function
    @n8ebel #androidsummit 71
    

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72. Local Functions
    4 Declare like any other function, but within an
    existing function
    4 Have access to all params and variables of the
    enclosing function
    @n8ebel #androidsummit 72
    

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73. Local Functions
    fun outerFunction(name:String) {
    fun innerFunction() {
    println(name)
    }
    ...
    innerFunction() // will print the passed name
    }
    @n8ebel #androidsummit 73
    

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74. Local Functions
    Why would you want this?
    4 Clean code
    4 Avoids code duplication
    4 Avoid deep chains of function calls
    @n8ebel #androidsummit 74
    

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75. Local Functions
    fun parseAccount(response:AccountResponse) : Account {
    ...
    val hobbies = response.getField("hobbies").map{
    val key = it.getField("key")
    Hobby(key)
    }
    val favoriteFoods = response.getField("favorite_foods").map{
    val key = it.getField("key")
    Food(key)
    }
    }
    @n8ebel #androidsummit 75
    

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76. Local Functions
    fun parseAccount(response:AccountResponse) : Account {
    fun parseKey(entity:ResponseEntity) = entity.getField("key")
    ...
    val hobbies = response.getField("hobbies").map{
    val key = parseKey(it)
    Hobby(key)
    }
    val favoriteFoods = response.getField("favorite_foods").map{
    val key = parseKey(it)
    Food(key)
    }
    }
    @n8ebel #androidsummit 76
    

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77. Local Function Considerations
    4 Local function or private method?
    4 Is the logic going to be needed outside the current
    function?
    4 Does the logic need to be tested in isolation?
    4 Is the enclosing function still readable?
    @n8ebel #androidsummit 77
    

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78. Companion Objects
    @n8ebel #androidsummit 78
    

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79. Companion Objects
    4 No static method/functions in Kotlin
    4 Recommended to use top-level functions instead
    4 What if you need access to private members of an
    object?
    @n8ebel #androidsummit 79
    

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80. Companion Objects
    4 Want to create a factory method?
    4 Define a member function on a companion object to
    gain access to private members/constructors
    @n8ebel #androidsummit 80
    

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81. Companion Objects: Use from Kotlin
    class Course private constructor(val key:String)
    // won't work
    // can't access the private constructor
    fun createCourse(key:String) : Course {
    return Course(key)
    }
    @n8ebel #androidsummit 81
    

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82. Companion Objects: Use from Kotlin
    class Course private constructor(val key:String) {
    companion object {
    fun createCourse(key:String) : Course {
    return Course(key)
    }
    }
    }
    @n8ebel #androidsummit 82
    

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83. Companion Objects: Use from Kotlin
    class Course private constructor(val key:String) {
    companion object {
    fun createCourse(key:String) : Course {
    return Course(key)
    }
    }
    }
    // can then call the factory method
    Course.createCourse("somekey")
    @n8ebel #androidsummit 83
    

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84. Companion Objects: Use From Java
    class AuthFragment : Fragment() {
    ...
    companion object {
    fun newInstance(username: String) = ...
    }
    }
    @n8ebel #androidsummit 84
    

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85. Companion Objects: Use From Java
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // explicitly reference `Companion` from Java
    AuthFragment.Companion.newInstance("username")
    }
    @n8ebel #androidsummit 85
    

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86. Companion Objects: Renaming
    Usage from Java is verbose
    AuthFragment.Companion.newInstance("username")
    @n8ebel #androidsummit 86
    

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87. Companion Objects: Renaming
    class AuthFragment : Fragment() {
    ...
    companion object Factory {
    fun newInstance(username: String) = ...
    }
    }
    AuthFragment.Factory.newInstance("username")
    @n8ebel #androidsummit 87
    

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88. Companion Objects: @JvmStatic
    class AuthFragment : Fragment() {
    ...
    companion object {
    @JvmStatic
    fun newInstance(username: String) = ...
    }
    }
    @n8ebel #androidsummit 88
    

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89. Companion Objects: @JvmStatic
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // no need to reference `Companion`
    AuthFragment.newInstance("username")
    }
    @n8ebel #androidsummit 89
    

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90. Variations
    @n8ebel #androidsummit 90
    

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91. Variations
    4 infix
    4 extension
    4 higher-order
    4 inline
    @n8ebel #androidsummit 91
    

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92. infix Functions
    @n8ebel #androidsummit 92
    

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93. infix Functions
    4 infix keyword enables usage of infix notation
    4 What is infix notation?
    4 Can omit the dot & parentheses for a function call
    4 "key" to "value"
    @n8ebel #androidsummit 93
    

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94. infix Functions
    4 Must be a member function or extension function
    4 Must take a single, non-varargs, parameter with no
    default value
    @n8ebel #androidsummit 94
    

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95. infix Functions
    class ConferenceAttendee {
    infix fun addInterest(name:String){...}
    }
    // call the function without dot or parentheses
    val attendee = ConferenceAttendee()
    attendee.addInterest("Kotlin")
    attendee addInterest "Kotlin"
    @n8ebel #androidsummit 95
    

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96. infix Functions
    4 Provides a very clean, human-readable syntax
    4 Core building block of custom DSLs
    @n8ebel #androidsummit 96
    

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97. infix Functions: stdlib
    for (i in 0 until 10 step 2) {
    println(i) // prints 0,2,4,6,8
    }
    "key" to someValue // creates a Pair
    var result: Boolean
    result = true or false // perform logical operations
    result = true and false
    @n8ebel #androidsummit 97
    

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98. infix Functions: Kotlin Test
    "hello" should haveSubstring("ell")
    "hello" shouldNot haveSubstring("olleh")
    https://github.com/kotlintest/kotlintest
    @n8ebel #androidsummit 98
    

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99. Extension Functions
    @n8ebel #androidsummit 99
    

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100. Extension Functions
     4 Extend the functionality of an existing class
     4 Defined outside the class
     4 Used as if they were a member of a class
     @n8ebel #androidsummit 100
     

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101. Why Extension Functions?
     4 Clean-up or extend classes & apis you don't control
     4 Remove helper classes & simplify top-level functions
     @n8ebel #androidsummit 101
     

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102. Extension Functions
     // add a new function to the View class
     fun View.isVisible() = visibility == View.VISIBLE
     yourView.isVisible()
     @n8ebel #androidsummit 102
     

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103. Extension Functions
     fun showToast(
     context: Context,
     msg:String,
     duration: Int = Toast.LENGTH_SHORT) {
     Toast.makeText(context, msg, duration).show()
     }
     showToast(context, "Toast!")
     @n8ebel #androidsummit 103
     

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104. Extension Functions
     fun Context.showToast(
     msg: CharSequence,
     duration: Int = Toast.LENGTH_SHORT) {
     Toast.makeText(this, msg, duration).show()
     }
     context.showToast("Toast!")
     @n8ebel #androidsummit 104
     

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105. Extension Function Considerations
     4 How are these generated under the hood?
     4 How are these called from Java?
     @n8ebel #androidsummit 105
     

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106. Extension Function Considerations
     4 Generated as static methods that accept the
     receiver object as it's first argument
     4 Default behavior is to use
     Kt.
     @n8ebel #androidsummit 106
     

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107. @n8ebel #androidsummit 107
     

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108. Extension Function Considerations
     // ContextExtensions.kt
     fun Context.showToast(...) { ... }
     // when called from Java
     ContextExtensionsKt.showToast(context, "Toast!");
     @n8ebel #androidsummit 108
     

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109. Higher-Order Functions
     @n8ebel #androidsummit 109
     

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110. Higher-Order Functions
     4 Functions that take, or return, other functions
     4 Can be lambda or function reference
     4 Many examples in the Kotlin standard library apply,
     also, run
     @n8ebel #androidsummit 110
     

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111. Higher-Order Functions
     4 Enable interesting patterns & conventions
     4 Support functional programming
     4 Can cleanup setup/teardown patterns such as
     shared prefs
     @n8ebel #androidsummit 111
     

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112. Higher-Order Functions
     fun getScoreCalculator(level:Level) {
     return when (level) {
     Level.EASY -> { state:ScoreState -> state.score * 10 }
     Level.HARD -> { state:ScoreState -> state.score * 5 * state.accuracy }
     }
     }
     @n8ebel #androidsummit 112
     

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113. Higher-Order Functions
     val predicate = { number:Int -> number > 5 }
     listOf(2,4,6,8).filter(predicate)
     @n8ebel #androidsummit 113
     

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114. Higher-Order Functions
     fun filterTheList(value:Int) = value > 5
     listOf(2,4,6,8).filter(::filterTheList)
     @n8ebel #androidsummit 114
     

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115. Higher-Order Functions
     If the last parameter of a function is a function, you
     can omit the parentheses
     listOf(2,4,6,8).filter{ number -> number > 5 }
     @n8ebel #androidsummit 115
     

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116. Higher-Order Functions
     public inline fun synchronized(lock: Any, block: () -> R): R {
     monitorEnter(lock)
     try {
     return block()
     }
     finally {
     monitorExit(lock)
     }
     }
     // call from Kotlin
     synchronized(database) {
     database.prePopulate()
     }
     @n8ebel #androidsummit 116
     

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117. Higher-Order Function Performance
     "Using higher-order functions imposes certain
     runtime penalties"
     4 Extra class created when using lambda
     4 If lambda captures variables, extra object created on
     each call
     @n8ebel #androidsummit 117
     

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118. inline Functions
     @n8ebel #androidsummit 118
     

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119. inline Functions
     4 Helps solve higher-order function performance hits
     4 Body of the inlined function is substituted for
     invocations of the function
     @n8ebel #androidsummit 119
     

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120. inline Functions
     inline fun synchronized(lock: Lock, action: () -> T): T {
     lock.lock()
     try {
     return action()
     }
     finally {
     lock.unlock()
     }
     }
     // call from Kotlin
     synchronized(Lock()) {...}
     @n8ebel #androidsummit 120
     

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121. inline Functions
     // sample usage
     fun inlineExample(l:Lock) {
     println("before")
     synchronized(l) {
     println("action")
     }
     println("after")
     }
     @n8ebel #androidsummit 121
     

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122. inline Functions
     With inline the generated code is equivalent to this
     // resulting code
     fun inlineExample(l:Lock) {
     println("before")
     lock.lock()
     try {
     println("action")
     }
     finally {
     lock.unlock()
     }
     println("after")
     }
     @n8ebel #androidsummit 122
     

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123. Android Reimagined
     @n8ebel #androidsummit 123
     

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124. Fewer Helper Classes
     4 ContextHelper, ViewUtils
     4 Replace with
     4 top-level functions
     4 extension functions
     @n8ebel #androidsummit 124
     

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125. Less Boilerplate
     fun doTheThingSafely(theThing:() -> Unit) {
     try {
     theThing()
     } catch(error:Throwable) {
     // handle error
     }
     }
     doTheThingSafely { unsafeFunction() }
     @n8ebel #androidsummit 125
     

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126. Upgrade Our Apis
     Can use extensions, default params, etc to cleanup/
     simplify/extend common apis
     4 Now seeing community supported examples of this
     4 Android KTX: https://github.com/android/android-
     ktx
     4 Anko: https://github.com/Kotlin/anko
     @n8ebel #androidsummit 126
     

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127. Android KTX
     sharedPreferences.edit()
     .putString("key", "without KTX")
     .putBoolean("isLessBoilerplate", false)
     .apply()
     sharedPreferences.edit {
     putString("key", "with KTX")
     putBoolean("isLessBoilerplate", true)
     }
     @n8ebel #androidsummit 127
     

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128. Android KTX
     // without KTX
     supportFragmentManager.beginTransaction()
     .replace(R.id.fragmentContainer, SomeFragment())
     .addToBackStack("name")
     .commit()
     // with KTX
     supportFragmentManager.transaction {
     replace(R.id.fagmentContainer, SomeFragment())
     addToBackStack("name")
     }
     @n8ebel #androidsummit 128
     

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129. Cleaner Syntax
     fun log(msg:String) {...}
     inline fun runOnBackgroundThread(action:() -> Unit) { ... }
     4 More fluent syntax
     4 Simplify test mocking
     4 Avoids extra classes
     @n8ebel #androidsummit 129
     

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130. Useful Collection Functions
     4 orEmpty()
     4 arrayOf(), listOf(), mapOf()
     4 associateBy(), groupBy()
     4 map(), mapIndexed()
     4 reduce(), sum(), filter(), partition()
     @n8ebel #androidsummit 130
     

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131. Useful Collection Functions
     // easily calculate sum from collection
     val totalDownloadSize = downloadRecords.sumBy { it.downloadSize }
     // sort all DownloadRecords based on download time
     val sortedDownloadEntities = downloadRecords.sortedByDescending { record ->
     record.downloadTime
     }
     @n8ebel #androidsummit 131
     

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132. Useful Collection Functions
     // return map with all DownloadRecords mapped to their parent enrollmentKey
     val entitiesGroupedByEnrollmentKey = downloadRecords.groupBy { record ->
     record.enrollmentKey
     }
     // ensure we have a non-null collection and map all records to view models
     val viewModels = inputRecords.orEmpty().map { record ->
     createViewModel(record)
     }
     @n8ebel #androidsummit 132
     

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133. Useful String Functions
     4 isEmpty(), isNotEmpty()
     4 substringBefore(), substringAfter()
     4 orEmpty()
     @n8ebel #androidsummit 133
     

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134. Useful String Functions
     if(!url.isNullOrEmpty()) {
     loadData(url)
     }
     viewModel.body = model.description.orEmpty()
     @n8ebel #androidsummit 134
     

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135. Kotlin functions provide
     flexibility & freedom in
     how you build your apps
     @n8ebel #androidsummit 135
     

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136. Go, and Have fun()
     4 Easy to get started with functions
     4 Flexibility gives convenience
     4 Enables us to reimagine how we build our apps
     @n8ebel #androidsummit 136
     

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137. Let's Continue the Discussion
     with("n8ebel").apply {
     Twitter
     YouTube
     .com
     Medium
     Facebook
     GitHub
     }
     @n8ebel #androidsummit 137
     

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138. Thanks For Coming
     @n8ebel #androidsummit 138
     

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