具有迭代器功能的Kotlin无限序列 [英] Kotlin infinite sequences with iterator function

问题描述

我对如何在Kotlin中创建一个无限序列用于惰性评估感到困惑.

I am confused about how to create an infinite sequence in Kotlin to use for lazy evaluation.

在Java中:

IntStream.iterate(0, i -> i + 2)
     .limit(100)
     .forEach(System.out::println);

，但是序列似乎比Java流更加混乱.序列构造函数非常令人困惑，因为它说:

but sequences seem much more confusing then Java streams. The sequence constructor is very confusing the doc for it says:

/**
 * Given an [iterator] function constructs a [Sequence] that returns values through the [Iterator]
 * provided by that function.
 * The values are evaluated lazily, and the sequence is potentially infinite.
 */

但我不知道迭代器函数的含义或如何制作迭代器函数.

but I don't know what it means by an iterator function or how to make one.

Sequence { iterator(arrayOf<Int>()) }
        .forEach { print(it) }

我有可以编译的文件，但是显然不打印任何东西.我认为我的迭代器函数没有任何意义.它需要一个不带任何参数并返回迭代器的函数，这根本不像Java .iterate函数.迭代器碰巧有一个采用数组的构造函数，如果我有要在数组中使用的数据集，那是有意义的，但我没有.我想使用无限序列.

I have this which compiles but obviously doesn't print anything. I don't think my iterator function makes any sense. It wants a function that takes no arguments and returns an iterator, which isn't like the Java .iterate function at all. Iterator happens to have a constructor that takes an array, which would make sense if I had a data set to work with in an array but I don't. I want to be working with an infinite sequence.

没有.limit，因此我以前尝试添加.reduce，但是.reduce的参数更加混乱.我认为应该有一个.toList，但是我知道它没有用，所以我没有尝试过.

There is no .limit, so I previously tried to add a .reduce but the arguments for .reduce were even more confusing. I think there should be a .toList but I knew it wasn't working so I didn't try it.

如果有人向我展示如何在Kotlin中实现上述Java代码，将会大有帮助.

If someone would show me how to implement the above Java code in Kotlin it would help a lot.

推荐答案

您可以使用

You can use generateSequence factory method:

generateSequence(0) { it + 2 }.forEach { println(it) }

或在特定情况下:

generateSequence(0) { it + 2 }.take(100).forEach { println(it) }

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