import type { Falsy, NonFalsy } from ".";
export declare class AssertError extends Error {
}
/** @example assert(typeof maybeString == "string", () => `Got ${typeof maybeString} instead of string`) */
export declare function assert<T>(value: T, message?: ((value: T & Falsy) => string) | string): asserts value;
/** Like typescript's non-null assertion operator (postfix `!`), but enforced at runtime.
  * @example ensure(objectOrUndefined, "Got undefined instead of object").property */
export declare const ensure: <T>(value: T, message?: ((value: T & Falsy) => string) | string) => NonFalsy<T>;