std@0.139.0/async/tee.ts

Deno standard library
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// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.// This module is browser compatible.
// Utility for representing n-tupletype Tuple<T, N extends number> = N extends N ? number extends N ? T[] : TupleOf<T, N, []> : never;type TupleOf<T, N extends number, R extends unknown[]> = R["length"] extends N ? R : TupleOf<T, N, [T, ...R]>;
interface QueueNode<T> { value: T; next: QueueNode<T> | undefined;}
class Queue<T> { #source: AsyncIterator<T>; #queue: QueueNode<T>; head: QueueNode<T>;
done: boolean;
constructor(iterable: AsyncIterable<T>) { this.#source = iterable[Symbol.asyncIterator](); this.#queue = { value: undefined!, next: undefined, }; this.head = this.#queue; this.done = false; }
async next(): Promise<void> { const result = await this.#source.next(); if (!result.done) { const nextNode: QueueNode<T> = { value: result.value, next: undefined, }; this.#queue.next = nextNode; this.#queue = nextNode; } else { this.done = true; } }}
/** * Branches the given async iterable into the n branches. * * Example: * * ```ts * import { tee } from "./tee.ts"; * * const gen = async function* gen() { * yield 1; * yield 2; * yield 3; * } * * const [branch1, branch2] = tee(gen()); * * (async () => { * for await (const n of branch1) { * console.log(n); // => 1, 2, 3 * } * })(); * * (async () => { * for await (const n of branch2) { * console.log(n); // => 1, 2, 3 * } * })(); * ``` */export function tee<T, N extends number = 2>( iterable: AsyncIterable<T>, n: N = 2 as N,): Tuple<AsyncIterable<T>, N> { const queue = new Queue<T>(iterable);
async function* generator(): AsyncGenerator<T> { let buffer = queue.head; while (true) { if (buffer.next) { buffer = buffer.next; yield buffer.value; } else if (queue.done) { return; } else { await queue.next(); } } }
const branches = Array.from({ length: n }).map( () => generator(), ) as Tuple< AsyncIterable<T>, N >; return branches;}