import type { PipeStep } from './pipe$.js';
import type { AnyAsyncIterable, AnyIterable, AsyncIteratedValue, IteratedValue } from './types/inputs/MinimalIterator.js';
import type { AnySubscribable } from './types/inputs/Subscribable.js';
import type { Observable } from './types/outputs/Observable.js';
import type { SimpleAsyncIterator, SimpleIterator } from './types/outputs/SimpleIterator.js';
/**
 * Flattens origin.
 *
 * @since 2.1.0
 * @version 2.5.0 Add support for async iterators
 */
export declare function flat$<O extends FlatOrigin>(): PipeStep<O, FlatResult<O, FlatResultValue<FlatOriginValue<O>>>>;
export type FlatOrigin<D = unknown> = AnyIterable<AnyIterable<D>> | AnyAsyncIterable<AnyIterable<D>> | AnySubscribable<AnyIterable<D>>;
export type FlatOriginValue<O extends FlatOrigin> = (O extends AnyIterable ? IteratedValue<O> : O extends AnyAsyncIterable ? AsyncIteratedValue<O> : unknown) & (O extends AnySubscribable<infer D> ? D : unknown);
export type FlatResult<O, R> = (O extends AnyIterable ? SimpleIterator<R> : O extends AnyAsyncIterable ? SimpleAsyncIterator<R> : unknown) & (O extends AnySubscribable ? Observable<R> : unknown);
export type FlatResultValue<D> = D extends AnyIterable ? IteratedValue<D> : unknown;