Kotlin: スコープ関数.md

概要

関数名	渡し方	参照	戻り値	例(val str = "hoge")
apply	関数	this	this	val strApply = str?.apply{ println( toUpperCase()) }
run	関数	this	結果の値	val upperStr = str?.run{ toUppserCase() }
let	関数	it	結果の値	val upperStr = str?.let{ it.toUppserCase() }
also	関数	it	this	val strAlso = str?.also{ println( it.toUpperCase()) }
with	引数	this	結果の値	val upperStr = with(str){ toUpperCase() }

apply

val listApply = mutableListOf<String>().apply {
 add("hoge")
 add("fuga")
}
println( "apply(1): $listApply" )

apply(1): [hoge, fuga]

with

val listWith = mutableListOf<String>()
with( listWith ) {
 add("hoge")
 add("fuga")
}
println( "with(1): $listWith" )

with(1): [hoge, fuga]

let

val listLet = mutableListOf<String>()
val ret = listLet.let {
 it.add( "hoge" )
 it.add( "fuga" )
}
println( "let(1): $listLet" )
println( "let(1): $ret" )

let(1): [hoge, fuga]
let(1): true

val listLet2 = mutableListOf<String>().let {
 it.add( "hoge" )
 it.add( "fuga" )
 it
}
println( "let(2): $listLet2" )

let(2): [hoge, fuga]

null でない場合だけ実行する

val listLet3: MutableList<String>? = null
listLet3?.let {
 it.add( "hoge" )
 it.add( "fuga" )
}
println( "let(3): $listLet3" )

let(3): null

run

val listRun = mutableListOf<String>()
val ret2 = listRun.run {
 add("hoge")
 add("fuga")
}
println( "run(1): $listRun" )
println( "run(1): $ret2" )

run(1): [hoge, fuga]
run(1): true

val listRun2 = mutableListOf<String>().run {
 add("hoge")
 add("fuga")
 this
}
println( "run(2): $listRun2" )

run(2): [hoge, fuga]