import { OperatorFunction, UnaryFunction } from 'rxjs';
/**
 * A mapping operator that only emits when the next value changes
 * @param project a projection function `(value: T) => R`
 * @returns an observable which value will be the return value of the projection function
 */
export declare function select<T, R>(project: UnaryFunction<T, R>): OperatorFunction<T, R>;