Kotlin:如何成对修改值? [英] Kotlin: How to modify a value in a pair?

问题描述

为什么不能更改该对中的值:

Why can't I change the values in the pair:

var p: Pair<Int, String> = Pair(5, "Test")
p.first = 3

p.first下的错误:无法重新分配Val

Error under p.first: Val cannot be reassigned

推荐答案

Pair 是不可变的.它的定义是有效的

Pair, like most data classes, is immutable. Its definition is effectively

data class Pair<out A, out B>(val first: A, val second: B)

如果它是可变的，则它在out A和out B中不能协变，也不能安全用作Map键.

If it were mutable, it could not be covariant in out A and out B, nor would it be safe to use as a Map key.

但是，与其他数据类一样，可以复制更改.

However, like other data classes, it can be copied with changes.

p = p.copy(first = 3)

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