import { Cache } from '../Cache';
import { CommonCacheOptions } from '../CommonCacheOptions';
import { KeyType } from '../KeyType';
import { WrappedCache } from '../WrappedCache';
import { Metrics } from './Metrics';
declare const METRICS: unique symbol;
/**
 * Options available for a metrics cache.
 */
export interface MetricsCacheOptions<K extends KeyType, V> extends CommonCacheOptions<K, V> {
    parent: Cache<K, V>;
}
/**
 * Extension to a cache that tracks metrics about the size and hit rate of
 * a cache.
 */
export declare class MetricsCache<K extends KeyType, V> extends WrappedCache<K, V> {
    private [METRICS];
    constructor(options: MetricsCacheOptions<K, V>);
    /**
     * Get metrics for this cache. Returns an object with the keys `hits`,
     * `misses` and `hitRate`. For caches that do not have metrics enabled
     * trying to access metrics will throw an error.
     *
     * @returns
     *   metrics of cache
     */
    get metrics(): Metrics;
    /**
     * Get the cached value for the specified key if it exists. Will return
     * the value or `null` if no cached value exist. Updates the usage of the
     * key.
     *
     * @param key -
     *   key to get
     * @returns
     *   current value or `null`
     */
    getIfPresent(key: K): V | null;
}
export {};