export declare function mustBeString(str: any, o?: any): string;
export declare function mustBeDefined<T>(t?: T, o?: any): T;
export declare function mustBeArray(str: any, o?: any): any[];
export declare function isArray(data: any): data is any[];
export declare function isNumber(data: any): data is number;
export declare function isString(data: any): data is string;
export declare const flattenMyArray: (arr: any[], result?: any[] | undefined) => any[];