import { TemplateRef } from '@angular/core';
import { BehaviorSubject } from 'rxjs';
import * as i0 from "@angular/core";
export type Overlays = Map<Symbol, TemplateRef<void>>;
export declare class OverlayService {
    overlays: BehaviorSubject<Overlays>;
    add(overlay: TemplateRef<void>): Promise<Symbol>;
    remove(key: Symbol): Promise<void>;
    static ɵfac: i0.ɵɵFactoryDeclaration<OverlayService, never>;
    static ɵprov: i0.ɵɵInjectableDeclaration<OverlayService>;
}