/** use this to ensure that all cases are covered in case of a selection */
/**
 * Verifies, that the given code path is never reached.
 * @example
 * ```ts
 * type Shape = Circle | Square;
 * function area(s: Shape): number {
 *   switch(s.type) {
 *     case 'circle': return Math.PI * s.radius ** 2;
 *     case 'square': return s.sideLength ** 2;
 *     default:       return assertUnreachable(s); // ensures that all cases are covered
 *   }
 * }
 * ```
 */
export declare function assertUnreachable(x: never): never;
/**
 * Verifies that the given value is not undefined.
 * This especially helps with a `.filter`
 * @example
 * ```ts
 * const values: (number | undefined)[] = [1, 2, undefined, 4];
 * const definedValues: number[] = values.filter(isNotUndefined);
 * // definedValues is now of type number[]
 * ```
 * @see {@link isUndefined}
 * @see {@link isNotNull}
 */
export declare function isNotUndefined<T>(this: void, x: T | undefined): x is T;
/**
 * Verifies that the given value is undefined.
 * This especially helps with a `.filter`
 * @example
 * ```ts
 * const values: (number | undefined)[] = [1, 2, undefined, 4];
 * const undefinedValues: undefined[] = values.filter(isUndefined);
 * // undefinedValues is now of type undefined[]
 * ```
 * @see {@link isNotUndefined}
 * @see {@link isNotNull}
 */
export declare function isUndefined<T>(this: void, x: T | undefined): x is undefined;
/**
 * Verifies that the given value is not null.
 * This especially helps with a `.filter`
 * @example
 * ```ts
 * const values: (number | null)[] = [1, 2, null, 4];
 * const nonNullValues: number[] = values.filter(isNotNull);
 * // nonNullValues is now of type number[]
 * ```
 * @see {@link isUndefined}
 * @see {@link isNotUndefined}
 */
export declare function isNotNull<T>(this: void, x: T | null): x is T;
/**
 * Generates a GitHub issue URL for reporting guard errors
 */
export declare function getGuardIssueUrl(message: string): string;
export type GuardMessage = string | (() => string);
/**
 * @param assertion   - will be asserted
 * @param message     - if a string, we will use it as the error message, if it is a function, we will call it to produce the error message (can be used to avoid costly message generations)
 * @throws GuardError - if the assertion fails
 */
export declare function guard(assertion: unknown | undefined, message?: GuardMessage): asserts assertion;