/**
 * Encapsulates definition of a parameter -- that is, its name and
 * its value. Parameters are used in request paths, request bodies,
 * querystrings, and as request headers.
 *
 * @public
 */
export default class Parameter {
    /**
     * @param {string} description
     * @param {string} key
     * @param {parameterValueCallback} extractor
     * @param {boolean=} optional
     */
    constructor(description: string, key: string, extractor: parameterValueCallback, optional?: boolean | undefined);
    /**
     * The human-readable description of the parameter.
     *
     * @public
     * @returns {string}
     */
    public get description(): string;
    /**
     * The name of the parameter.
     *
     * @public
     * @returns {string}
     */
    public get key(): string;
    /**
     * A function for extracting the parameter's value.
     *
     * @public
     * @returns {parameterValueCallback}
     */
    public get extractor(): parameterValueCallback;
    /**
     * Indicates if the parameter is required.
     *
     * @public
     * @returns {boolean}
     */
    public get optional(): boolean;
    /**
     * Throws an {@link Error} if the instance is invalid.
     *
     * @public
     */
    public validate(): void;
    /**
     * Returns a string representation.
     *
     * @public
     * @returns {string}
     */
    public toString(): string;
    #private;
}
/**
 * A function that, when passed the request's payload, returns a parameter's value.
 */
export type parameterValueCallback = (payload: object) => Promise<string>;