node_modules/rxjs/src/internal/Operator.ts

import { Subscriber } from './Subscriber';
import { TeardownLogic } from './types';

/***
 * @deprecated Internal implementation detail, do not use directly. Will be made internal in v8.
 */
export interface Operator<T, R> {
  call(subscriber: Subscriber<R>, source: any): TeardownLogic;
}