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val mutableList vs var List

Last updated at Posted at 2018-08-30

どう違うのか?
試してみましょう


	val items1 = mutableListOf(1,2,3)
    println(items1.toString())  // [1, 2, 3]
    items1 = mutableListOf(10)  // Error:(9, 4) Val cannot be reassigned
    items1.add(4)
    println(items1.toString())  // [1, 2, 3, 4]

    var items2 = listOf(1,2,3)
    items2.add(4)               // Error:(10, 11) Unresolved reference: add
    println(items2.toString())  // [1, 2, 3]
    items2 = listOf(11)
    println(items2.toString())  // [11]

varは最代入可能な通常の変数、valはfinalに置き換わるので再代入が不可能な変数。mutableListは普通のListになるのでaddが可能、Listはイミュータブル扱いになるので、addはできない。
というふうに整理できるのですね

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