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Property + Getter
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scache
July 03, 2018
Programming
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1.4k
Property + Getter
Kotlin
Property + Getter
scache
July 03, 2018
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Transcript
Property + Getter ू·ΕKotlin͖ʂKotlinѪձ vol2 scache( @scal_ch )
About me • scache ( @scal_ch ) • Android/Kotlin •
AbemaTV
val + getter vs fun val isEmpty get() = size
== 0 or fun isEmpty() = size == 0
Properties • var/val • var/val + custom getter • Property
Delegation(e.g. lazy)
var (not null) class Var(var varHoge: String = “var”) Var().let
{ it.varHoge.toList() }
val(not null) class Val(val valHoge: String = "not null") Val().let
{ it.valHoge.toList() }
var class Var(var varHoge: String? = “var”) Var().let { it.varHoge
?: return@let it.varHoge toList() }
var class Var(var varHoge: String? = “var”) Var().let { it.varHoge
?: return@let it.varHoge?.toList() }
val class Val(val valHoge: String? = "not null") Val().let {
it.valHoge ?: return@let it.valHoge toList() }
val class Val(val valHoge: String? = "not null") Val().let {
it.valHoge ?: return@let it.valHoge.toList() }
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() }
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() }
val + custom getter class ValGetter( var hoge: String? =
"not null" ) { val valNullable: String? get() = hoge } ValGetter().let { it.valNullable ?: return@let it.valNullable toList() }
val + custom getter class ValGetter( var hoge: String? =
"not null" ) { val valNullable: String? get() = hoge } ValGetter().let { it.valNullable ?: return@let it.valNullable?.toList() }
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
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
val + lazy class LazyVal { val hoge: String? by
lazy { "not null" } } LazyVal().let { it.hoge ?: return@let it.hoge toList() }
val + lazy class LazyVal { val hoge: String? by
lazy { "not null" } } LazyVal().let { it.hoge ?: return@let it.hoge?.toList() }
val + getter vs fun val isEmpty get() = size
== 0 or fun isEmpty() = size == 0
Kotlin Πϯ ΞΫγϣϯʹΑΔͱ Ҿͷͳ͍ؔͱΧελϜGetterΛ࣋ͭϓϩύςΟՄಡੑ ʹͷΈҧ͍͕͋Δ
Kotlin Πϯ ΞΫγϣϯʹΑΔͱ Ҿͷͳ͍ؔͱΧελϜGetterΛ࣋ͭϓϩύςΟՄಡੑ ʹͷΈҧ͍͕͋Δ hoge.isEmpty or hoge.isEmpty()
Kotlin Πϯ ΞΫγϣϯʹΑΔͱ Ҿͷͳ͍ؔͱΧελϜGetterΛ࣋ͭϓϩύςΟՄಡੑ ʹͷΈҧ͍͕͋Δ ΫϥεͷಛΛදݱ͍ͨ͠߹ʹϓϩύςΟʹ͢Δ
kotlin-stdlib public val <T> List<T>.lastIndex: Int get() = this.size -
1
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
·ͱΊ ݸਓతͳҙݟ • valมͷ࣮Λݟͳ͍ͱ͕ෆม͔Ͳ͏͔ෆ໌ • Functions vs Properties ͷϧʔϧʹै͏ •
໎ͬͨΒfun • ผͷҙݟฉ͖͍ͨͷͰ࠙ձͰ͓ئ͍͠·͢ʂ
None
͓·͚ J2K Branch A 1. javaϑΝΠϧΛίϐʔͯ͠ktϑΝΠϧΛ࡞ 2. ktϑΝΠϧΛमਖ਼ 3. javaϑΝΠϧΛফͯ͠ίϛοτ
Branch B 1. javaϑΝΠϧΛktϑΝΠϧʹϦωʔϜͯ͠ίϛοτ 2. ktϑΝΠϧͷ༰ΛBranchA͔Β͖࣋ͬͯͯίϛοτ