import type { AsyncOptLazy, MaybePromise } from '@rimbu/common';
/**
 * An asynchronous iterator that extends the default `AsyncIterator` interface with methods for improved performance.
 * @typeparam T - the element type
 */
export interface AsyncFastIterator<T> extends AsyncIterator<T> {
    /**
     * Returns the next iterator value asynchronously, or the given `otherwise` `AsyncOptLazy` value instead.
     */
    fastNext(): MaybePromise<T | undefined>;
    /**
     * Returns the next iterator value asynchronously, or the given `otherwise` `AsyncOptLazy` value instead.
     * @param otherwise - (default: undefined) the value to return if the iterator has no more values
     * @typeparam O - the type of the alternative value
     */
    fastNext<O>(otherwise: AsyncOptLazy<O>): MaybePromise<T | O>;
    /**
     * Returns a promise resolving to the next `IteratorResult`.
     */
    next(): Promise<IteratorResult<T>>;
}