在Kotlin中生成带有Lambda的列表 [英] Generate a list with lambdas in kotlin

问题描述

我是Kotlin和lambdas的新手，我正试图了解它.我正在尝试生成100个随机数的列表. 这有效:

I'm new to Kotlin and lambdas and I'm trying to understand it. I'm trying to generate a list of 100 random numbers. This works:

private val maxRandomValues = (1..100).toList()

但是我想做这样的事情:

But I want to do something like that:

private val maxRandomValues = (1..100).forEach { RandomGenerator().nextDouble() }.toList()

但是这不起作用.我试图弄清楚如何使用在toList()

But this is not working. I'm trying to figure out how to use the values generated into forEach are used in the toList()

推荐答案

使用kotlin.collections函数执行此操作更好:

It's way better to use kotlin.collections function to do this:

List(100) {
    Random.nextInt()
}

根据Collections.kt

inline fun <T> List(size: Int, init: (index: Int) -> T): List<T> = MutableList(size, init)

还可以根据您的情况生成使用范围:

It's also possible to generate using range like in your case:

(1..100).map { Random.nextInt() }

不能使用forEach的原因是它返回Unit(在Java，C#等中类似于void). map操作Iterable(在这种情况下为1至100的数字range)将它们映射为另一个值.然后，它将返回包含所有这些值的列表.在这种情况下，使用上面的List构造函数更有意义，因为您并不是真正地映射"值，而是创建一个列表

The reason you can't use forEach is that it return Unit (which is sort of like void in Java, C#, etc.). map operates Iterable (in this case the range of numbers from 1 to 100) to map them to a different value. It then returns a list with all those values. In this case, it makes more sense to use the List constructor above because you're not really "mapping" the values, but creating a list

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