如何在javascript中克隆迭代器？ [英] How to clone an Iterator in javascript?

问题描述

在ES6中，有没有可能克隆迭代器状态？

In ES6, is there any possible to clone an iterator states?

var ma=[1,2,3,4];
var it=ma[Symbol.iterator]();
it.next();

如果我想在这里记住，它说明我应该如何在javascritp中做什么？

if I want to remember here the it states how should I do in javascritp?

它的重新编号是什么？
自

what is remebered in it? since the

JSON.stringify(it) //it would just return {}

推荐答案

您不能克隆任意迭代器，但可以从中创建许多不同的迭代器保持一些状态：

You can’t clone an arbitrary iterator, but you can create many distinct iterators from one by holding onto some state:

function tee(iterable) {
    const source = iterable[Symbol.iterator]();
    const buffers = [[], []];  // substitute in queue type for efficiency
    const DONE = Object.create(null);

    const next = i => {
        if (buffers[i].length !== 0) {
            return buffers[i].shift();
        }

        const x = source.next();

        if (x.done) {
            return DONE;
        }

        buffers[1 - i].push(x.value);
        return x.value;
    };

    return buffers.map(function* (_, i) {
        for (;;) {
            const x = next(i);

            if (x === DONE) {
                break;
            }

            yield x;
        }
    });
}

用法：

const [a, b] = tee(iterator);
assert(a.next().value === b.next().value);

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