Property + Getter

Kotlin
Property + Getter

Transcript

1. Property + Getter
   ू·ΕKotlin޷͖ʂKotlinѪ޷ձ vol2
   scache( @scal_ch )
   

   View Slide

2. About me
   • scache ( @scal_ch )
   
   • Android/Kotlin
   
   • AbemaTV
   

   View Slide

3. val + getter vs fun
   val isEmpty get() = size == 0
   or
   fun isEmpty() = size == 0
   

   View Slide

4. Properties
   • var/val
   
   • var/val + custom getter
   
   • Property Delegation(e.g. lazy)
   

   View Slide

5. var (not null)
   class Var(var varHoge: String = “var”)
   Var().let {
   it.varHoge.toList()
   }
   

   View Slide

6. val(not null)
   class Val(val valHoge: String = "not null")
   Val().let {
   it.valHoge.toList()
   }
   

   View Slide

7. var
   class Var(var varHoge: String? = “var”)
   Var().let {
   it.varHoge ?: return@let
   it.varHoge toList()
   }
   

   View Slide

8. var
   class Var(var varHoge: String? = “var”)
   Var().let {
   it.varHoge ?: return@let
   it.varHoge?.toList()
   }
   

   View Slide

9. val
   class Val(val valHoge: String? = "not null")
   Val().let {
   it.valHoge ?: return@let
   it.valHoge toList()
   }
   

   View Slide

10. val
    class Val(val valHoge: String? = "not null")
    Val().let {
    it.valHoge ?: return@let
    it.valHoge.toList()
    }
    

    View Slide

11. var + custom getter
    class VarGetter {
    val rand = Random()
    var varGetter: String? = null
    get() = "random: ${rand.nextInt()}"
    }
    VarGetter().let {
    it.varGetter ?: return@let
    it.varGetter toList()
    }
    

    View Slide

12. var + custom getter
    class VarGetter {
    val rand = Random()
    var varGetter: String? = null
    get() = "random: ${rand.nextInt()}"
    }
    VarGetter().let {
    it.varGetter ?: return@let
    it.varGetter?.toList()
    }
    

    View Slide

13. val + custom getter
    class ValGetter(
    var hoge: String? = "not null"
    ) {
    val valNullable: String?
    get() = hoge
    }
    ValGetter().let {
    it.valNullable ?: return@let
    it.valNullable toList()
    }
    

    View Slide

14. val + custom getter
    class ValGetter(
    var hoge: String? = "not null"
    ) {
    val valNullable: String?
    get() = hoge
    }
    ValGetter().let {
    it.valNullable ?: return@let
    it.valNullable?.toList()
    }
    

    View Slide

15. Declaring Properties
    These can be declared as mutable, using the var keyword
    or read-only using the val keyword.
    https://kotlinlang.org/docs/reference/properties.html#declaring-properties
    

    View Slide

16. Declaring Properties
    These can be declared as mutable, using the var keyword
    or read-only using the val keyword.
    https://kotlinlang.org/docs/reference/properties.html#declaring-properties
    

    View Slide

17. val + lazy
    class LazyVal {
    val hoge: String? by lazy { "not null" }
    }
    LazyVal().let {
    it.hoge ?: return@let
    it.hoge toList()
    }
    

    View Slide

18. val + lazy
    class LazyVal {
    val hoge: String? by lazy { "not null" }
    }
    LazyVal().let {
    it.hoge ?: return@let
    it.hoge?.toList()
    }
    

    View Slide

19. val + getter vs fun
    val isEmpty get() = size == 0
    or
    fun isEmpty() = size == 0
    

    View Slide

20. Kotlin Πϯ ΞΫγϣϯʹΑΔͱ
    Ҿ਺ͷͳ͍ؔ਺ͱΧελϜGetterΛ࣋ͭϓϩύςΟ͸Մಡੑ
    ʹͷΈҧ͍͕͋Δ
    

    View Slide

21. Kotlin Πϯ ΞΫγϣϯʹΑΔͱ
    Ҿ਺ͷͳ͍ؔ਺ͱΧελϜGetterΛ࣋ͭϓϩύςΟ͸Մಡੑ
    ʹͷΈҧ͍͕͋Δ
    
    hoge.isEmpty
    or
    hoge.isEmpty()
    

    View Slide

22. Kotlin Πϯ ΞΫγϣϯʹΑΔͱ
    Ҿ਺ͷͳ͍ؔ਺ͱΧελϜGetterΛ࣋ͭϓϩύςΟ͸Մಡੑ
    ʹͷΈҧ͍͕͋Δ
    
    Ϋϥεͷಛ௃Λදݱ͍ͨ͠৔߹ʹ͸ϓϩύςΟʹ͢Δ
    

    View Slide

23. kotlin-stdlib
    public val List.lastIndex: Int
    get() = this.size - 1
    

    View Slide

24. Functions vs Properties
    Prefer a property one a function when the underlying
    algorithm
    
    • does not throw
    
    • is cheap to calculate
    
    • returns the same result over innovations if the object state
    hasn’t changed
    
    https://kotlinlang.org/docs/reference/coding-conventions.html#functions-vs-properties
    

    View Slide

25. ·ͱΊ
    ݸਓతͳҙݟ
    
    • valม਺ͷ࣮૷Λݟͳ͍ͱ஋͕ෆม͔Ͳ͏͔ෆ໌
    
    • Functions vs Properties ͷϧʔϧʹै͏
    
    • ໎ͬͨΒfun
    
    • ผͷҙݟ΋ฉ͖͍ͨͷͰ࠙਌ձͰ͓ئ͍͠·͢ʂ
    

    View Slide

26. View Slide

27. ͓·͚ J2K
    Branch A
    
    1. javaϑΝΠϧΛίϐʔͯ͠ktϑΝΠϧΛ࡞੒
    
    2. ktϑΝΠϧΛमਖ਼
    
    3. javaϑΝΠϧΛফͯ͠ίϛοτ
    
    Branch B
    
    1. javaϑΝΠϧΛktϑΝΠϧʹϦωʔϜͯ͠ίϛοτ
    
    2. ktϑΝΠϧͷ಺༰ΛBranchA͔Β͖࣋ͬͯͯίϛοτ
    

    View Slide