import { type HttpResponseParts, TO_HTTP_RESPONSE_PARTS, type ToHttpResponseParts } from "./to-response-parts.js";
/**
 * Represents a unique identifier for an extension, defined by a symbol.
 *
 * The `ExtensionKey` class provides a way to create and manage keys for
 * extensions that are associated with a specific type, ensuring type safety and
 * uniqueness.
 *
 * @example
 * ```ts
 * import { ExtensionKey } from "taxum/core/http";
 *
 * type MyExtensionValue = { foo: string };
 * const MY_EXTENSION = new ExtensionKey<MyExtensionValue>("My extension");
 * ```
 */
export declare class ExtensionKey<T> {
    private readonly _type;
    private readonly description;
    constructor(description: string);
    toJSON(): string;
}
/**
 * A map for setting and retrieving extensions.
 *
 * The accessors use {@link ExtensionKey}s to guarantee type-safety with the
 * associated values.
 */
export declare class Extensions implements ToHttpResponseParts {
    private readonly map;
    /**
     * Inserts a value into the map associated with a specific key.
     */
    insert<T>(key: ExtensionKey<T>, value: T): void;
    /**
     * Retrieves the value associated with the specified key from the map.
     */
    get<T>(key: ExtensionKey<T>): T | undefined;
    /**
     * Removes a value associated with the specified key from the map.
     */
    remove<T>(key: ExtensionKey<T>): void;
    /**
     * Determines whether the specified key exists in the map.
     */
    has<T>(key: ExtensionKey<T>): boolean;
    /**
     * Clears all key-value pairs from the map.
     */
    clear(): void;
    /**
     * Checks whether the map is empty.
     */
    isEmpty(): boolean;
    /**
     * Retrieves the size of the map.
     */
    len(): number;
    /**
     * Extends the current instance with entries from another instance.
     */
    extend(other: Extensions): this;
    [TO_HTTP_RESPONSE_PARTS](res: HttpResponseParts): void;
    toJSON(): Record<string, unknown>;
}