Type aliases in Kotlin allow defining an alias for an existing type. This helps simplify generic types and function signatures. The document discusses using type aliases to define a Weight type as a Double to represent weights in kilograms for classes like Human and Dog. It also shows how to extend the Weight type with properties and functions to work with grams by defining an extension on the Kg type alias. This allows classes that use the Weight type to interact with weights in grams through the Kg alias without needing to know the underlying type is Double.

1. Type aliases
5 Kotlin Sansan
2017 4/4
Kamedon

3. •
• Kotlin
•
•

5. Type aliases

6. // ラムダ式を省略、簡単に
typealias Action<T> = (T) -> Unit
• function types with complex signatures:
UserAction = (User, Context) ->
ActionResponse,
• complex generic types: Multimap<K, V> =
Map<K, List<V>>
Type aliases

7. typealias Action<T> = (T) -> Unit
fun <T> T.action(action: Action<T>) {
action(this)
}
"test".action { print(it) }
"test".action(::print)
val action: (String) -> Unit = { print(it) }
"test".action(printAction)

10. Type aliases
typealias Weight = Double
class Human(val weight: Weight)
class Dog(val weight: Weight)
• weight
• Weight Double kg,g

11. Type aliases
typealias Weight = Double
class Human(val weight: Weight)
class Dog(val weight: Weight)
• weight
• Weight Double kg,g

12. Type aliases
typealias Weight = Double
class Human(val weight: Weight)
class Dog(val weight: Weight)
• weight
• Weight Double kg,g

13. Type aliases
typealias Weight = Double
class Human(val weight: Weight)
class Dog(val weight: Weight)
typealias Length = Double
val length: Length = 173.0
Human(length)
• value class

15. Type aliases
typealias Kg = Double
class Human(val weight: Kg)
class Dog(val weight: Kg)
• Weight kg
•

16. Type Aliases
//拡張プロパティ
val Kg.g get() = this * 1000
//拡張関数
fun Kg.g() = this * 1000
•
print(Human(60.0).weight.g())
print(Human(60.0).weight.g())

17. oh ..
print(10.0.g)
print(10.0.g())
• !! …
• Kg
Double

19. interface
interface Weight {
//拡張プロパティ
val Kg.g get() = this * 1000
//拡張関数
fun Kg.g() = this * 1000
}
• interface Weight
• inteface Double

20. interface
class Human(val weight: Kg) : Weight {
fun showWeight() {
print(weight.g)
}
}
class Dog(val weight: Kg){
fun showWeight() {
print(weight.g)
}
}

21. …
interface Weight {
typealias Kg = Double
}
• Type aliases

23. • Type aliases
•
•
• Type aliases
• interface

24. • Android Studio 2.3
• Kotlin 1.1.1