Kotlin数据类中可变集合的防御性副本 [英] Defensive copy of a mutable collection in Kotlin data class

问题描述

我想让一个数据类接受一个只读列表:

I want to have a data class accepting a read-only list:

data class Notebook(val notes: List<String>) {
}

但是它也可以接受MutableList，因为它是List的子类型.

But it can accept MutableList as well, because it is a subtype of the List.

例如，以下代码修改了传入列表:

For example the following code modifies the passed in list:

fun main(args: Array<String>) {
    val notes = arrayListOf("One", "Two")
    val notebook = Notebook(notes)

    notes.add("Three")

    println(notebook)       // prints: Notebook(notes=[One, Two, Three])
}

有没有一种方法可以对数据类中的传入列表进行防御性复制?

Is there a way how perform defensive copy of the passed in list in the data class?

推荐答案

我认为最好将JetBrains库用于不可变集合- https://github.com/Kotlin/kotlinx.collections.immutable

I think better is to use JetBrains library for immutable collections - https://github.com/Kotlin/kotlinx.collections.immutable

导入您的项目

添加Bintray存储库:

Add the bintray repository:

repositories {
    maven {
        url "http://dl.bintray.com/kotlin/kotlinx"
    }
}

添加依赖项:

compile 'org.jetbrains.kotlinx:kotlinx-collections-immutable:0.1'

结果:

data class Notebook(val notes: ImmutableList<String>) {}

fun main(args: Array<String>) {
    val notes = immutableListOf("One", "Two")
    val notebook = Notebook(notes)

    notes.add("Three") // creates a new collection

    println(notebook)       // prints: Notebook(notes=[One, Two])
}

注意: 您还可以在ImmutableList中使用add和remove方法，但是此方法不会修改当前列表，只是使用您的更改创建一个新列表并为您返回.

Note: You also can use add and remove methods with ImmutableList, but this methods doesn't modify current list just creates new one with your changes and return it for you.

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