import { Func, Nillable, NonNil } from "./types";
export declare const strings: {
    is: (value: any) => boolean;
    requireNonNil: (value: string | null | undefined, message?: string | (() => Error)) => NonNil<string>;
    requireNonNilElse: (value: Nillable<string>, defaultValue?: NonNil<string> | Func<Nillable<string>, string>) => NonNil<string>;
    isNilOrEmpty: (value: Nillable<string>) => boolean;
    isNilOrWhitespace: (value: Nillable<string>) => boolean;
};