ix/asynciterable/operators/memoize.mjs

The Interactive Extensions for JavaScript

import { __asyncGenerator, __await } from "tslib";
import { AsyncIterableX } from '../asynciterablex.mjs';
import { MaxRefCountList, RefCountList, } from '../../iterable/operators/_refcountlist.mjs';
import { create } from '../create.mjs';
import { throwIfAborted } from '../../aborterror.mjs';
/** @ignore */
export class MemoizeAsyncBuffer extends AsyncIterableX {
    constructor(source, buffer) {
        super();
        this._error = null;
        this._shared = null;
        this._stopped = false;
        this._source = source;
        this._buffer = buffer;
    }
    [Symbol.asyncIterator](signal) {
        throwIfAborted(signal);
        return this._getIterable(0);
    }
    _getIterable(offset = 0) {
        return __asyncGenerator(this, arguments, function* _getIterable_1() {
            let i = offset - 1;
            let done = false;
            const buffer = this._buffer;
            try {
                do {
                    if (++i < buffer.count) {
                        yield yield __await(buffer.get(i));
                        continue;
                    }
                    if (this._stopped) {
                        throw this._error;
                    }
                    if (this._shared === null) {
                        this._shared = this._source.next().then((r) => {
                            this._shared = null;
                            if (!r.done) {
                                buffer.push(r.value);
                            }
                            return r;
                        });
                    }
                    ({ done } = yield __await(this._shared.catch((e) => {
                        this._error = e;
                        this._stopped = true;
                        throw e;
                    })));
                    if (!done) {
                        yield yield __await(buffer.get(i));
                    }
                } while (!done);
            }
            finally {
                buffer.done();
            }
        });
    }
}
/**
 * Memoizes the source sequence within a selector function where a specified number of iterators can get access
 * to all of the sequence's elements without causing multiple iterations over the source.
 *
 * @template TSource Source sequence element type.
 * @template TResult Result sequence element type.
 * @param {number} [readerCount=-1] Number of iterators that can access the underlying buffer. Once every
 * iterator has obtained an element from the buffer, the element is removed from the buffer.
 * @param {(value: AsyncIterable<TSource>) => AsyncIterable<TResult>} [selector] Selector function with memoized access
 * to the source sequence for a specified number of iterators.
 * @returns {(OperatorAsyncFunction<TSource, TSource | TResult>)} Sequence resulting from applying the selector function to the
 * memoized view over the source sequence.
 */
export function memoize(readerCount = -1, selector) {
    return function memoizeOperatorFunction(source) {
        if (!selector) {
            return readerCount === -1
                ? new MemoizeAsyncBuffer(source[Symbol.asyncIterator](), new MaxRefCountList())
                : new MemoizeAsyncBuffer(source[Symbol.asyncIterator](), new RefCountList(readerCount));
        }
        return create(() => selector(memoize(readerCount)(source))[Symbol.asyncIterator]());
    };
}

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