/**
 * Throws an `Err.ForcedError` error when called.
 * @example
 * ```ts
 * const emptyMap = HashMap.empty<number, string>()
 * emptyMap.get(5, Err);
 * // throws: Err.CustomError(message: 'Err: forced to throw error')
 * ```
 */
export declare function Err(): never;
export declare namespace ErrBase {
    /**
     * A custom error instance.
     */
    abstract class CustomError {
        readonly message: string;
        constructor(message: string);
        get name(): string;
    }
    class ForcedError extends CustomError {
    }
    /**
     * Returns a function that, when called, throws an `Err.ForcedError` with the given `message` string.
     * @param message - the message to put in the `Err.ForcedError` instance.
     * @example
     * ```ts
     * const emptyMap = HashMap.empty<number, string>()
     * emptyMap.get(5, ErrBase.msg('not found'));
     * // throws: Err.CustomError(message: 'not found')
     * ```
     */
    function msg(message: string): () => never;
}