shelving/sequence/LazyDeferredSequence.js

Toolkit for using data in JavaScript.

import { Starter } from "../util/start.js";
import { DeferredSequence } from "./DeferredSequence.js";
import { IteratorSequence } from "./IteratorSequence.js";
/** Deferred sequence of values that calls a `StartCallback` when it has iterators that are iterating, and calls the corresponding `StopCallback` when all iterators have finished. */
export class LazyDeferredSequence extends DeferredSequence {
    _iterating = 0;
    _starter;
    constructor(start) {
        super();
        this._starter = new Starter(start);
    }
    // biome-ignore lint/suspicious/useAwait: We want the method to be async but we're using `yield*` rather than `await`
    async *[Symbol.asyncIterator]() {
        this._starter.start(this);
        this._iterating++;
        try {
            // Delegate to the superclass's async iterator.
            // Wrap in an `IteratorSequence` because we know the superclass `AbstractSequence.prototype.[Symbol.asyncIterator]()` simply returns `this`
            // `yield* this` would call this method again and cause an infinite loop.
            yield* new IteratorSequence(super[Symbol.asyncIterator]());
        }
        finally {
            this._iterating--;
            if (this._iterating < 1)
                this._starter.stop();
        }
    }
    [Symbol.dispose]() {
        this._starter[Symbol.dispose]();
    }
}