/**
 * @license
 * Copyright Google LLC All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */
/**
 * A token used to manipulate and access values stored in `HttpContext`.
 *
 * @publicApi
 */
export declare class HttpContextToken<T> {
    readonly defaultValue: () => T;
    constructor(defaultValue: () => T);
}
/**
 * Http context stores arbitrary user defined values and ensures type safety without
 * actually knowing the types. It is backed by a `Map` and guarantees that keys do not clash.
 *
 * This context is mutable and is shared between cloned requests unless explicitly specified.
 *
 * @usageNotes
 *
 * ### Usage Example
 *
 * ```typescript
 * // inside cache.interceptors.ts
 * export const IS_CACHE_ENABLED = new HttpContextToken<boolean>(() => false);
 *
 * export class CacheInterceptor implements HttpInterceptor {
 *
 *   intercept(req: HttpRequest<any>, delegate: HttpHandler): Observable<HttpEvent<any>> {
 *     if (req.context.get(IS_CACHE_ENABLED) === true) {
 *       return ...;
 *     }
 *     return delegate.handle(req);
 *   }
 * }
 *
 * // inside a service
 *
 * this.httpClient.get('/api/weather', {
 *   context: new HttpContext().set(IS_CACHE_ENABLED, true)
 * }).subscribe(...);
 * ```
 *
 * @publicApi
 */
export declare class HttpContext {
    private readonly map;
    /**
     * Store a value in the context. If a value is already present it will be overwritten.
     *
     * @param token The reference to an instance of `HttpContextToken`.
     * @param value The value to store.
     *
     * @returns A reference to itself for easy chaining.
     */
    set<T>(token: HttpContextToken<T>, value: T): HttpContext;
    /**
     * Retrieve the value associated with the given token.
     *
     * @param token The reference to an instance of `HttpContextToken`.
     *
     * @returns The stored value or default if one is defined.
     */
    get<T>(token: HttpContextToken<T>): T;
    /**
     * Delete the value associated with the given token.
     *
     * @param token The reference to an instance of `HttpContextToken`.
     *
     * @returns A reference to itself for easy chaining.
     */
    delete(token: HttpContextToken<unknown>): HttpContext;
    /**
     * Checks for existence of a given token.
     *
     * @param token The reference to an instance of `HttpContextToken`.
     *
     * @returns True if the token exists, false otherwise.
     */
    has(token: HttpContextToken<unknown>): boolean;
    /**
     * @returns a list of tokens currently stored in the context.
     */
    keys(): IterableIterator<HttpContextToken<unknown>>;
}