Kotlinもう一歩

Kotlinのタイプシステムとジェネリクスについて

Transcript

1. Hiroyuki Mori
   @moridroid
   Kotlinもう一歩
   

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2. 本書きました！
   

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3. goo.gl/fW2YPh
   

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4. Kotlinもう一歩
   

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5. Kotlinのタイプシステム
   

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6. クラスとタイプ
   

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7. クラス ≠ タイプ
   

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8. // class: String, type: String
   val s1: String = "string"
   

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9. // class: String, type: String
   val s1: String = "string"
   // class: String, type: String?
   val s2 : String? = "string"
   

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10. タイプとは何か
    

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11. ・すべての変数や式には型がある
    // type: String
    val str : String = "string"
    // type: Char
    if (str.isNotEmpty()) str[0] else '\n'
    

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12. ・型によって、変数や式のとりうる値の範囲が決まる
    // type: String　→ 文字列
    val str : String = "string"
    // type: Char　→ 16-bit ユニコード文字
    if (str.isNotEmpty()) str[0] else '\n'
    

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13. ・型によって、行える演算や操作が決まる
    // 文字列は加算できる
    val s = "abc" + "def"
    // 整数はいろいろできる
    val i = 100 * (10 - 2) / (30 + 1)
    

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14. ・型によって、行える演算や操作が決まる
    // OK
    val str1 : String = "string"
    str1.hashCode()
    // nullableはいろいろできない
    val str2 : String? = "string"
    str2.hashCode() // NG
    

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15. だから安全！
    

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16. タイプとサブタイプ
    

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17. タイプAが期待されるすべての箇所で、
    タイプBが使用可能であれば、
    BはAのサブタイプ
    B このとき、AはBのスーパータイプ
    

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18. val c : CharSequence = "abc" // OK
    fun foo(c : CharSequence) {}
    foo("abc") // OK
    fun bar() : CharSequence = "abc" // OK
    

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19. val c : CharSequence = "abc" // OK
    fun foo(c : CharSequence) {}
    foo("abc") // OK
    fun bar() : CharSequence = "abc" // OK
    

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20. val c : CharSequence = "abc" // OK
    fun foo(c : CharSequence) {}
    foo("abc") // OK
    fun bar() : CharSequence = "abc" // OK
    

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21. // Int val num1 : Number = 100
    // Double val num2 : Number = 10.0
    // Long val num3 : Number = 100L
    

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22. Int, Long, Double, … Number
    Long Int
    Double Float
    Short
    Byte
    

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23. Int型はNumber型の範囲内
    Number
    Int
    OK
    Long Int
    Double Float
    Short
    Byte
    

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24. Number型は、Int型の範囲内とは限らない
    Number
    Int
    NG
    Long Int
    Double Float
    Short
    Byte DoubleやLongかも？
    

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25. クイズ
    

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26. Kotlinのタイプシステムでは、
    Int型はInt型の…
    (A) サブタイプ
    (B) スーパータイプ
    (C) どちらでもない
    (D) どちらでもある
    

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27. Kotlinのタイプシステムでは、
    Int型はInt型の…
    (A) サブタイプ
    (B) スーパータイプ
    (C) どちらでもない
    (D) どちらでもある
    

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28. In Kotlin in Action
    

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30. val intType = Int::class.createType()
    intType.isSubtypeOf(intType)
    > true
    intType.isSupertypeOf(intType)
    > true
    

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32. Any
    

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33. // Int val any1 : Any = 100
    // Double val any2 : Any = 10.0
    // String val any3 : Any = "str"
    

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34. // String? val any4 : Any = null as String?
    

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36. Nothing
    

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37. // Why does this work?
    fun bar() : Int = TODO()
    

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38. // Why does this work?
    fun bar() : Int = TODO()
    val str1 : String = TODO()
    fun foo(l : List) = {}
    foo(TODO())
    

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39. public inline fun TODO(): Nothing =
    throw NotImplementedError()
    public class Nothing private constructor()
    

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40. fun nothing() : Nothing =
    throw Exception("nothing")
    val a : Number = nothing()
    val b : String = nothing()
    val c : List = nothing()
    

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42. nullableとnon-null
    

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43. // String val str1 : String? = "str" // OK
    fun foo(s : String?) {}
    foo("abc") // OK
    fun bar() : String? = "abc" // OK
    

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44. // String val str1 : String? = "str" // OK
    // String? val str2 : String = str1
    // NonNull

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46. まとめ
    

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48. Generics
    

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49. fun toString(i : Int) = i.toString()
    fun toString(l : Long) = l.toString()
    fun toString(f : Float) = d.toString()
    ...
    

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50. fun toString(t : T) = t.toString()
    

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51. fun toDouble(i : Int) = i.toDouble()
    fun toDouble(l : Long) = l.toDouble()
    fun toDouble(f : Float) = f.toDouble()
    ...
    

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52. fun toDouble(t : T) = t.toDouble()
    

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53. 上限境界
    

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54. fun toDouble(t : T)
    = t.toDouble()
    

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55. fun copyWhenGreater(list: List, threshold: T)
    : List
    where T : CharSequence,
    T : Comparable {
    return list.filter { it > threshold }
    .map { it.toString() }
    }
    

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56. fun copyWhenGreater(list: List, threshold: T)
    : List
    where T : CharSequence,
    T : Comparable {
    return list.filter { it > threshold }
    .map { it.toString() }
    }
    

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57. 型引数とnullability
    

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58. fun foo(t : T) = t.hashCode()
    

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59. fun foo(t : T) = t.hashCode()
    

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60. fun foo(t : T) = t.hashCode()
    fun foo(t : T) = t?.hashCode()
    

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61. Type Erasure
    

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62. // Kotlin Code: List
    val list : List = listOf()
    

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63. // Kotlin Code: List
    val list : List = listOf()
    // Decompiled : List
    List list = CollectionsKt.emptyList();
    

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64. if (list is List) {
    // You can't do this
    }
    

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65. 変位
    

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66. Int

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67. Int val number : Number = 123
    

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68. Int List
    

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69. Int List
    val nums : List = listOf(1, 2, 3)
    

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70. Int List
    MutableList
    

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71. Int List
    MutableList
    val nums : MutableList = mutableListOf(1, 2, 3)
    

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72. タイプAが期待されるすべての箇所で、
    タイプBが使用可能であれば、
    BはAのサブタイプ
    

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73. MutableListは、
    MutableListの
    代わりに使えない場合がある
    

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74. // もしこれが可能なら
    val nums : MutableList
    = mutableListOf(1, 2, 3)
    // これができてしまう
    nums.add(10.5)
    

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75. val nums = mutableListOf(1, 2, 3)
    val ints = mutableListOf(1, 2, 3)
    val num1 : Number = nums[0] // OK
    val num2 : Number = ints[0] // OK
    nums.add(10.0) // OK
    ints.add(10.0) // NG
    

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76. 変位
    B Foo と Fooにどういう関係があるか
    

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77. invariant, covariant, contravariant
    　不変　　　共変　　　　反変　　　
    

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78. invariant, covariant, contravariant
    B Foo でもなく
    Foo でもない
    

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79. class Invariant(val value : T)
    invariant, covariant, contravariant
    

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80. class Invariant(val value : T)
    val num : Invariant
    = Invariant(100)
    

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81. class Invariant(val value : T)
    val num : Invariant
    = Invariant(100)
    val int : Invariant
    = Invariant(100)
    

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82. invariant, covariant, contravariant
    B
    

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83. invariant, covariant, contravariant
    class Covariant(val value: T)
    

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84. class Covariant(val value: T)
    val num : Covariant
    = Covariant(100)
    invariant, covariant, contravariant
    

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85. class Covariant(val value: T)
    val num : Covariant
    = Covariant(100)
    val int : Covariant
    = Covariant(100)
    invariant, covariant, contravariant
    

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86. invariant, covariant, contravariant
    B
    

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87. class Contravariant(value: T)
    invariant, covariant, contravariant
    

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88. class Contravariant(value: T)
    val num : Contravariant
    = Contravariant(100)
    invariant, covariant, contravariant
    

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89. class Contravariant(value: T)
    val num : Contravariant
    = Contravariant(100)
    val int : Contravariant
    = Contravariant(10.0)
    invariant, covariant, contravariant
    

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90. 不変 共変 反変
    
    サブタイプを
    引き継がない
    サブタイプを
    引き継ぐ
    サブタイプが
    逆転する
    

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91. inとout
    

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92. out
    

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93. class Covariant (t: T) {
    val value1 = t
    var value2 = t
    fun get() : T = value1
    fun set(t: T) { value2 = t }
    }
    

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94. class Covariant (t: T) {
    val value = t
    fun get() : T = value
    }
    

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95. val num1 : Number = 100
    val num2 : Number
    = Covariant(100).get()
    

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96. public interface List : Collection {
    

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97. in
    

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98. class Contravariant (t: T) {
    val value1 = t
    var value2 = t
    fun get() : T = value1
    fun set(t: T) { }
    }
    

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99. class Contravariant (t: T) {
    fun set(t: T) { }
    }
    

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100. val num = Contravariant(100)
     num.set(1234567L)
     num.set(10.0)
     num.set(123) // OK!
     

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101. class Contravariant (t: T) {
     fun set(t: T) { }
     }
     

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102. class Contravariant (t: T) {
     private var value : T = t
     private fun get() : T = value
     fun set(t: T) { value = t }
     }
     

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103. 不変 共変 反変
     
     サブタイプを
     引き継がない
     サブタイプを
     引き継ぐ
     サブタイプが
     逆転する
     Tは
     どこでも使用可
     Tは
     戻り値だけ
     Tは
     引数だけ
     

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104. Type Projection
     

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105. MutableList
     

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106. MutableList
     val nums : MutableList
     = mutableListOf(1, 2, 3)
     

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107. MutableList
     val nums : MutableList
     = mutableListOf(1, 2, 3)
     val nums : MutableList
     = mutableListOf(1.0, 2.0, 3.0)
     

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108. class Foo
     val foo : Foo
     class Bar
     val bar : Bar
     

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109. 余談
     

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110. val nums : MutableList
     = mutableListOf(1, 2, 3)
     

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111. val nums : MutableList = mutableListOf(1, 2, 3)
     val constructor = Nothing::class.java.getDeclaredConstructor()
     constructor.isAccessible = true
     val nothing = constructor.newInstance()
     

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112. val nums : MutableList = mutableListOf(1, 2, 3)
     val constructor = Nothing::class.java.getDeclaredConstructor()
     constructor.isAccessible = true
     val nothing = constructor.newInstance()
     nums.add(nothing)
     

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113. val nums : MutableList = mutableListOf(1, 2, 3)
     val constructor = Nothing::class.java.getDeclaredConstructor()
     constructor.isAccessible = true
     val nothing = constructor.newInstance()
     nums.add(nothing)
     print(nums)
     > [1, 2, 3, java.lang.Void@5e9d7b78]
     

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114. Star Projection
     

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115. // Java Way
     List> list;
     

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116. // Java Way
     List> list;
     // Kotlin Way
     val list : List
     

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117. // Java Way
     List> list;
     // Kotlin Way
     val list : List // List
     

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118. // List
     val list : List = listOf(1, 2, 3)
     // This is safe
     val foo : Any? = list[0]
     

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119. // MutableList
     val list : MutableList
     = mutableListOf(1, 2, 3)
     // This is not safe
     list.add(4.0)
     

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120. Star Projection
     と変位アノテーション
     

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121. out
     

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122. class Foo(val value : T)
     

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123. class Foo(val value : T)
     val foo : Foo = Foo(1)
     

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124. class Foo(val value : T)
     val foo : Foo = Foo(1)
     // Foo
     

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125. in
     

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126. class Foo {
     fun foo(t : T) {}
     }
     

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127. class Foo {
     fun foo(t : T) {}
     }
     val foo : Foo = Foo()
     

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128. class Foo {
     fun foo(t : T) {}
     }
     val foo : Foo = Foo()
     // Foo
     

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129. class Foo {
     fun foo(t : T) {}
     }
     val foo : Foo = Foo()
     // Foo
     

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131. class Foo {
     fun foo(t : T) {}
     }
     val foo : Foo = Foo()
     // Foo
     

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132. class Foo {
     fun foo(t : T) {}
     }
     val foo : Foo = Foo()
     // Foo
     foo.foo(1) // requires Nothing
     

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133. invariant
     

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134. class Foo {
     fun foo() : T = TODO()
     fun bar(t : T) {}
     }
     

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135. class Foo {
     fun foo() : T = TODO()
     fun bar(t : T) {}
     }
     val foo : Foo = Foo()
     

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136. class Foo {
     fun foo() : T = TODO()
     fun bar(t : T) {}
     }
     val foo : Foo = Foo()
     val n = foo.foo() // Foo
     

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137. class Foo {
     fun foo() : T = TODO()
     fun bar(t : T) {}
     }
     val foo : Foo = Foo()
     val n = foo.foo() // Foo
     foo.bar(n) // Foo
     

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138. まとめ
     

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139. 不変 共変 反変
     
     サブタイプを
     引き継がない
     サブタイプを
     引き継ぐ
     サブタイプが
     逆転する
     Tは
     どこでも使用可
     Tは
     戻り値だけ
     Tは
     引数だけ
     

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140. class Foo
     Foo // Foo
     class Bar
     Bar // Bar
     

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141. class Foo
     Foo // Foo
     class Bar
     Bar // Bar
     

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142. class Foo
     Foo // Foo : out position
     // Foo : in position
     class Bar
     Bar // Bar : out position
     // Bar : in position
     

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143. Hiroyuki Mori
     @moridroid
     Thank you
     

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