export type SafeFunction = (...args: unknown[]) => unknown;
export declare class TypeSpecifier {
    isUndefined(data: unknown): data is undefined;
    isNull(data: unknown): data is null;
    isNumber(data: unknown): data is number;
    isString(data: unknown): data is string;
    isBigInt(data: unknown): data is bigint;
    isError(data: unknown): data is Error;
    isFunction(data: unknown): data is SafeFunction;
    isArray(data: unknown): data is unknown[];
    isObject(data: unknown): data is object;
    private hasImplementedToString;
}