/**
 * @module LRUCache
 */
export type Perf = {
    now: () => number;
};
declare const TYPE: unique symbol;
export type PosInt = number & {
    [TYPE]: 'Positive Integer';
};
export type Index = number & {
    [TYPE]: 'LRUCache Index';
};
export type UintArray = Uint8Array | Uint16Array | Uint32Array;
export type NumberArray = UintArray | number[];
declare class ZeroArray extends Array<number> {
    constructor(size: number);
}
export type { ZeroArray };
export type { Stack };
export type StackLike = Stack | Index[];
declare class Stack {
    #private;
    heap: NumberArray;
    length: number;
    static create(max: number): StackLike;
    constructor(max: number, HeapCls: {
        new (n: number): NumberArray;
    });
    push(n: Index): void;
    pop(): Index;
}
/**
 * Promise representing an in-progress {@link LRUCache#fetch} call
 */
export type BackgroundFetch<V> = Promise<V | undefined> & {
    __returned: BackgroundFetch<V> | undefined;
    __abortController: AbortController;
    __staleWhileFetching: V | undefined;
};
export type DisposeTask<K, V> = [
    value: V,
    key: K,
    reason: LRUCache.DisposeReason
];
export declare namespace LRUCache {
    /**
     * An integer greater than 0, reflecting the calculated size of items
     */
    type Size = number;
    /**
     * Integer greater than 0, representing some number of milliseconds, or the
     * time at which a TTL started counting from.
     */
    type Milliseconds = number;
    /**
     * An integer greater than 0, reflecting a number of items
     */
    type Count = number;
    /**
     * The reason why an item was removed from the cache, passed
     * to the {@link Disposer} methods.
     *
     * - `evict`: The item was evicted because it is the least recently used,
     *   and the cache is full.
     * - `set`: A new value was set, overwriting the old value being disposed.
     * - `delete`: The item was explicitly deleted, either by calling
     *   {@link LRUCache#delete}, {@link LRUCache#clear}, or
     *   {@link LRUCache#set} with an undefined value.
     * - `expire`: The item was removed due to exceeding its TTL.
     * - `fetch`: A {@link OptionsBase#fetchMethod} operation returned
     *   `undefined` or was aborted, causing the item to be deleted.
     */
    type DisposeReason = 'evict' | 'set' | 'delete' | 'expire' | 'fetch';
    /**
     * A method called upon item removal, passed as the
     * {@link OptionsBase.dispose} and/or
     * {@link OptionsBase.disposeAfter} options.
     */
    type Disposer<K, V> = (value: V, key: K, reason: DisposeReason) => void;
    /**
     * The reason why an item was added to the cache, passed
     * to the {@link Inserter} methods.
     *
     * - `add`: the item was not found in the cache, and was added
     * - `update`: the item was in the cache, with the same value provided
     * - `replace`: the item was in the cache, and replaced
     */
    type InsertReason = 'add' | 'update' | 'replace';
    /**
     * A method called upon item insertion, passed as the
     * {@link OptionsBase.insert}
     */
    type Inserter<K, V> = (value: V, key: K, reason: InsertReason) => void;
    /**
     * A function that returns the effective calculated size
     * of an entry in the cache.
     */
    type SizeCalculator<K, V> = (value: V, key: K) => Size;
    /**
     * Options provided to the
     * {@link OptionsBase.fetchMethod} function.
     */
    interface FetcherOptions<K, V, FC = unknown> {
        signal: AbortSignal;
        options: FetcherFetchOptions<K, V, FC>;
        /**
         * Object provided in the {@link FetchOptions.context} option to
         * {@link LRUCache#fetch}
         */
        context: FC;
    }
    /**
     * Occasionally, it may be useful to track the internal behavior of the
     * cache, particularly for logging, debugging, or for behavior within the
     * `fetchMethod`. To do this, you can pass a `status` object to the
     * {@link LRUCache#fetch}, {@link LRUCache#get}, {@link LRUCache#set},
     * {@link LRUCache#memo}, and {@link LRUCache#has} methods.
     *
     * The `status` option should be a plain JavaScript object. The following
     * fields will be set on it appropriately, depending on the situation.
     *
     * These objects are also the context objects passed to listeners on the
     * `lru-cache:metrics` diagnostic channel, and the `lru-cache` tracing
     * channels, in platforms that support them.
     */
    interface Status<K, V> {
        /**
         * The operation being performed
         */
        op?: 'get' | 'set' | 'memo' | 'fetch' | 'delete' | 'has' | 'peek';
        /**
         * The status of a set() operation.
         *
         * - add: the item was not found in the cache, and was added
         * - update: the item was in the cache, with the same value provided
         * - replace: the item was in the cache, and replaced
         * - miss: the item was not added to the cache for some reason
         */
        set?: 'add' | 'update' | 'replace' | 'miss' | 'deleted';
        /**
         * The status of a delete() operation.
         */
        delete?: LRUCache.DisposeReason;
        /**
         * The result of a peek() operation
         *
         * - hit: the item was found and returned
         * - stale: the item is in the cache, but past its ttl and not returned
         * - miss: item not in the cache
         */
        peek?: 'hit' | 'miss' | 'stale';
        /**
         * The status of a memo() operation.
         *
         * - 'hit': the item was found in the cache and returned
         * - 'miss': the `memoMethod` function was called
         */
        memo?: 'hit' | 'miss';
        /**
         * The `context` option provided to a memo or fetch operation
         *
         * In practice, of course, this will be the same type as the `FC`
         * fetch context param used to instantiate the LRUCache, but the
         * convolutions of threading that through would get quite complicated,
         * and preclude forcing/forbidding the passing of a `context` param
         * where it is/isn't expected, which is more valuable for error
         * prevention.
         */
        context?: unknown;
        /**
         * the ttl stored for the item, or undefined if ttls are not used.
         */
        ttl?: Milliseconds;
        /**
         * the start time for the item, or undefined if ttls are not used.
         */
        start?: Milliseconds;
        /**
         * The timestamp used for TTL calculation
         */
        now?: Milliseconds;
        /**
         * the remaining ttl for the item, or undefined if ttls are not used.
         */
        remainingTTL?: Milliseconds;
        /**
         * The calculated size for the item, if sizes are used.
         */
        entrySize?: Size;
        /**
         * The total calculated size of the cache, if sizes are used.
         */
        totalCalculatedSize?: Size;
        /**
         * A flag indicating that the item was not stored, due to exceeding the
         * {@link OptionsBase.maxEntrySize}
         */
        maxEntrySizeExceeded?: true;
        /**
         * The key that was set or retrieved
         */
        key?: K;
        /**
         * The value that was set
         */
        value?: V;
        /**
         * The old value, specified in the case of `set:'replace'`
         */
        oldValue?: V;
        /**
         * The results of a {@link LRUCache#has} operation
         *
         * - hit: the item was found in the cache
         * - stale: the item was found in the cache, but is stale
         * - miss: the item was not found in the cache
         */
        has?: 'hit' | 'stale' | 'miss';
        /**
         * The status of a {@link LRUCache#fetch} operation.
         * Note that this can change as the underlying fetch() moves through
         * various states.
         *
         * - inflight: there is another fetch() for this key which is in process
         * - get: there is no {@link OptionsBase.fetchMethod}, so
         *   {@link LRUCache#get} was called.
         * - miss: the item is not in cache, and will be fetched.
         * - hit: the item is in the cache, and was resolved immediately.
         * - stale: the item is in the cache, but stale.
         * - refresh: the item is in the cache, and not stale, but
         *   {@link FetchOptions.forceRefresh} was specified.
         */
        fetch?: 'get' | 'inflight' | 'miss' | 'hit' | 'stale' | 'refresh';
        /**
         * `forceRefresh` option was used for either a fetch or memo operation
         */
        forceRefresh?: boolean;
        /**
         * The {@link OptionsBase.fetchMethod} was called
         */
        fetchDispatched?: true;
        /**
         * The cached value was updated after a successful call to
         * {@link OptionsBase.fetchMethod}
         */
        fetchUpdated?: true;
        /**
         * The reason for a fetch() rejection.  Either the error raised by the
         * {@link OptionsBase.fetchMethod}, or the reason for an
         * AbortSignal.
         */
        fetchError?: Error;
        /**
         * The fetch received an abort signal
         */
        fetchAborted?: true;
        /**
         * The abort signal received was ignored, and the fetch was allowed to
         * continue in the background.
         */
        fetchAbortIgnored?: true;
        /**
         * The fetchMethod promise resolved successfully
         */
        fetchResolved?: true;
        /**
         * The fetchMethod promise was rejected
         */
        fetchRejected?: true;
        /**
         * The status of a {@link LRUCache#get} operation.
         *
         * - fetching: The item is currently being fetched.  If a previous value
         *   is present and allowed, that will be returned.
         * - stale: The item is in the cache, and is stale. If it was returned,
         *   then the `returnedStale` flag will be set.
         * - stale-fetching: The value is being fetched in the background, but is
         *   currently stale. If the stale value was returned, then the
         *   `returnedStale` flag will be set.
         * - hit: the item is in the cache
         * - miss: the item is not in the cache
         */
        get?: 'stale' | 'hit' | 'miss' | 'fetching' | 'stale-fetching';
        /**
         * A fetch or get operation returned a stale value.
         */
        returnedStale?: true;
        /**
         * A tracingChannel trace was started for this operation
         */
        trace?: boolean;
    }
    /**
     * options which override the options set in the LRUCache constructor
     * when calling {@link LRUCache#fetch}.
     *
     * This is the union of {@link GetOptions} and {@link SetOptions}, plus
     * {@link OptionsBase.noDeleteOnFetchRejection},
     * {@link OptionsBase.allowStaleOnFetchRejection},
     * {@link FetchOptions.forceRefresh}, and
     * {@link FetcherOptions.context}
     *
     * Any of these may be modified in the {@link OptionsBase.fetchMethod}
     * function, but the {@link GetOptions} fields will of course have no
     * effect, as the {@link LRUCache#get} call already happened by the time
     * the fetchMethod is called.
     */
    interface FetcherFetchOptions<K, V, FC = unknown> extends Pick<OptionsBase<K, V, FC>, 'allowStale' | 'updateAgeOnGet' | 'noDeleteOnStaleGet' | 'sizeCalculation' | 'ttl' | 'noDisposeOnSet' | 'noUpdateTTL' | 'noDeleteOnFetchRejection' | 'allowStaleOnFetchRejection' | 'ignoreFetchAbort' | 'allowStaleOnFetchAbort'> {
        status?: Status<K, V>;
        size?: Size;
    }
    /**
     * Options that may be passed to the {@link LRUCache#fetch} method.
     */
    interface FetchOptions<K, V, FC> extends FetcherFetchOptions<K, V, FC> {
        /**
         * Set to true to force a re-load of the existing data, even if it
         * is not yet stale.
         */
        forceRefresh?: boolean;
        /**
         * Context provided to the {@link OptionsBase.fetchMethod} as
         * the {@link FetcherOptions.context} param.
         *
         * If the FC type is specified as unknown (the default),
         * undefined or void, then this is optional.  Otherwise, it will
         * be required.
         */
        context?: FC;
        signal?: AbortSignal;
        status?: Status<K, V>;
    }
    /**
     * Options provided to {@link LRUCache#fetch} when the FC type is something
     * other than `unknown`, `undefined`, or `void`
     */
    interface FetchOptionsWithContext<K, V, FC> extends FetchOptions<K, V, FC> {
        context: FC;
    }
    /**
     * Options provided to {@link LRUCache#fetch} when the FC type is
     * `undefined` or `void`
     */
    interface FetchOptionsNoContext<K, V> extends FetchOptions<K, V, undefined> {
        context?: undefined;
    }
    interface MemoOptions<K, V, FC = unknown> extends Pick<OptionsBase<K, V, FC>, 'allowStale' | 'updateAgeOnGet' | 'noDeleteOnStaleGet' | 'sizeCalculation' | 'ttl' | 'noDisposeOnSet' | 'noUpdateTTL' | 'noDeleteOnFetchRejection' | 'allowStaleOnFetchRejection' | 'ignoreFetchAbort' | 'allowStaleOnFetchAbort'> {
        /**
         * Set to true to force a re-load of the existing data, even if it
         * is not yet stale.
         */
        forceRefresh?: boolean;
        /**
         * Context provided to the {@link OptionsBase.memoMethod} as
         * the {@link MemoizerOptions.context} param.
         *
         * If the FC type is specified as unknown (the default),
         * undefined or void, then this is optional.  Otherwise, it will
         * be required.
         */
        context?: FC;
        status?: Status<K, V>;
    }
    /**
     * Options provided to {@link LRUCache#memo} when the FC type is something
     * other than `unknown`, `undefined`, or `void`
     */
    interface MemoOptionsWithContext<K, V, FC> extends MemoOptions<K, V, FC> {
        context: FC;
    }
    /**
     * Options provided to {@link LRUCache#memo} when the FC type is
     * `undefined` or `void`
     */
    interface MemoOptionsNoContext<K, V> extends MemoOptions<K, V, undefined> {
        context?: undefined;
    }
    /**
     * Options provided to the
     * {@link OptionsBase.memoMethod} function.
     */
    interface MemoizerOptions<K, V, FC = unknown> {
        options: MemoizerMemoOptions<K, V, FC>;
        /**
         * Object provided in the {@link MemoOptions.context} option to
         * {@link LRUCache#memo}
         */
        context: FC;
    }
    /**
     * options which override the options set in the LRUCache constructor
     * when calling {@link LRUCache#memo}.
     *
     * This is the union of {@link GetOptions} and {@link SetOptions}, plus
     * {@link MemoOptions.forceRefresh}, and
     * {@link MemoOptions.context}
     *
     * Any of these may be modified in the {@link OptionsBase.memoMethod}
     * function, but the {@link GetOptions} fields will of course have no
     * effect, as the {@link LRUCache#get} call already happened by the time
     * the memoMethod is called.
     */
    interface MemoizerMemoOptions<K, V, FC = unknown> extends Pick<OptionsBase<K, V, FC>, 'allowStale' | 'updateAgeOnGet' | 'noDeleteOnStaleGet' | 'sizeCalculation' | 'ttl' | 'noDisposeOnSet' | 'noUpdateTTL'> {
        status?: Status<K, V>;
        size?: Size;
        start?: Milliseconds;
    }
    /**
     * Options that may be passed to the {@link LRUCache#has} method.
     */
    interface HasOptions<K, V, FC> extends Pick<OptionsBase<K, V, FC>, 'updateAgeOnHas'> {
        status?: Status<K, V>;
    }
    /**
     * Options that may be passed to the {@link LRUCache#get} method.
     */
    interface GetOptions<K, V, FC> extends Pick<OptionsBase<K, V, FC>, 'allowStale' | 'updateAgeOnGet' | 'noDeleteOnStaleGet'> {
        status?: Status<K, V>;
    }
    /**
     * Options that may be passed to the {@link LRUCache#peek} method.
     */
    interface PeekOptions<K, V, FC> extends Pick<OptionsBase<K, V, FC>, 'allowStale'> {
        status?: Status<K, V>;
    }
    /**
     * Options that may be passed to the {@link LRUCache#set} method.
     */
    interface SetOptions<K, V, FC> extends Pick<OptionsBase<K, V, FC>, 'sizeCalculation' | 'ttl' | 'noDisposeOnSet' | 'noUpdateTTL'> {
        /**
         * If size tracking is enabled, then setting an explicit size
         * in the {@link LRUCache#set} call will prevent calling the
         * {@link OptionsBase.sizeCalculation} function.
         */
        size?: Size;
        /**
         * If TTL tracking is enabled, then setting an explicit start
         * time in the {@link LRUCache#set} call will override the
         * default time from `performance.now()` or `Date.now()`.
         *
         * Note that it must be a valid value for whichever time-tracking
         * method is in use.
         */
        start?: Milliseconds;
        status?: Status<K, V>;
    }
    /**
     * The type signature for the {@link OptionsBase.fetchMethod} option.
     */
    type Fetcher<K, V, FC = unknown> = (key: K, staleValue: V | undefined, options: FetcherOptions<K, V, FC>) => Promise<V | undefined | void> | V | undefined | void;
    /**
     * the type signature for the {@link OptionsBase.memoMethod} option.
     */
    type Memoizer<K, V, FC = unknown> = (key: K, staleValue: V | undefined, options: MemoizerOptions<K, V, FC>) => V;
    /**
     * Options which may be passed to the {@link LRUCache} constructor.
     *
     * Most of these may be overridden in the various options that use
     * them.
     *
     * Despite all being technically optional, the constructor requires that
     * a cache is at minimum limited by one or more of {@link OptionsBase.max},
     * {@link OptionsBase.ttl}, or {@link OptionsBase.maxSize}.
     *
     * If {@link OptionsBase.ttl} is used alone, then it is strongly advised
     * (and in fact required by the type definitions here) that the cache
     * also set {@link OptionsBase.ttlAutopurge}, to prevent potentially
     * unbounded storage.
     *
     * All options are also available on the {@link LRUCache} instance, making
     * it safe to pass an LRUCache instance as the options argumemnt to
     * make another empty cache of the same type.
     *
     * Some options are marked as read-only, because changing them after
     * instantiation is not safe. Changing any of the other options will of
     * course only have an effect on subsequent method calls.
     */
    interface OptionsBase<K, V, FC> {
        /**
         * The maximum number of items to store in the cache before evicting
         * old entries. This is read-only on the {@link LRUCache} instance,
         * and may not be overridden.
         *
         * If set, then storage space will be pre-allocated at construction
         * time, and the cache will perform significantly faster.
         *
         * Note that significantly fewer items may be stored, if
         * {@link OptionsBase.maxSize} and/or {@link OptionsBase.ttl} are also
         * set.
         *
         * **It is strongly recommended to set a `max` to prevent unbounded growth
         * of the cache.**
         */
        max?: Count;
        /**
         * Max time in milliseconds for items to live in cache before they are
         * considered stale.  Note that stale items are NOT preemptively removed by
         * default, and MAY live in the cache, contributing to its LRU max, long
         * after they have expired, unless {@link OptionsBase.ttlAutopurge} is
         * set.
         *
         * If set to `0` (the default value), then that means "do not track
         * TTL", not "expire immediately".
         *
         * Also, as this cache is optimized for LRU/MRU operations, some of
         * the staleness/TTL checks will reduce performance, as they will incur
         * overhead by deleting items.
         *
         * This is not primarily a TTL cache, and does not make strong TTL
         * guarantees. There is no pre-emptive pruning of expired items, but you
         * _may_ set a TTL on the cache, and it will treat expired items as missing
         * when they are fetched, and delete them.
         *
         * Optional, but must be a non-negative integer in ms if specified.
         *
         * This may be overridden by passing an options object to `cache.set()`.
         *
         * At least one of `max`, `maxSize`, or `TTL` is required. This must be a
         * positive integer if set.
         *
         * Even if ttl tracking is enabled, **it is strongly recommended to set a
         * `max` to prevent unbounded growth of the cache.**
         *
         * If ttl tracking is enabled, and `max` and `maxSize` are not set,
         * and `ttlAutopurge` is not set, then a warning will be emitted
         * cautioning about the potential for unbounded memory consumption.
         * (The TypeScript definitions will also discourage this.)
         */
        ttl?: Milliseconds;
        /**
         * Minimum amount of time in ms in which to check for staleness.
         * Defaults to 1, which means that the current time is checked
         * at most once per millisecond.
         *
         * Set to 0 to check the current time every time staleness is tested.
         * (This reduces performance, and is theoretically unnecessary.)
         *
         * Setting this to a higher value will improve performance somewhat
         * while using ttl tracking, albeit at the expense of keeping stale
         * items around a bit longer than their TTLs would indicate.
         *
         * @default 1
         */
        ttlResolution?: Milliseconds;
        /**
         * Preemptively remove stale items from the cache.
         *
         * Note that this may *significantly* degrade performance, especially if
         * the cache is storing a large number of items. It is almost always best
         * to just leave the stale items in the cache, and let them fall out as new
         * items are added.
         *
         * Note that this means that {@link OptionsBase.allowStale} is a bit
         * pointless, as stale items will be deleted almost as soon as they
         * expire.
         *
         * Use with caution!
         */
        ttlAutopurge?: boolean;
        /**
         * When using time-expiring entries with `ttl`, setting this to `true` will
         * make each item's age reset to 0 whenever it is retrieved from cache with
         * {@link LRUCache#get}, causing it to not expire. (It can still fall out
         * of cache based on recency of use, of course.)
         *
         * Has no effect if {@link OptionsBase.ttl} is not set.
         *
         * This may be overridden by passing an options object to `cache.get()`.
         */
        updateAgeOnGet?: boolean;
        /**
         * When using time-expiring entries with `ttl`, setting this to `true` will
         * make each item's age reset to 0 whenever its presence in the cache is
         * checked with {@link LRUCache#has}, causing it to not expire. (It can
         * still fall out of cache based on recency of use, of course.)
         *
         * Has no effect if {@link OptionsBase.ttl} is not set.
         */
        updateAgeOnHas?: boolean;
        /**
         * Allow {@link LRUCache#get} and {@link LRUCache#fetch} calls to return
         * stale data, if available.
         *
         * By default, if you set `ttl`, stale items will only be deleted from the
         * cache when you `get(key)`. That is, it's not preemptively pruning items,
         * unless {@link OptionsBase.ttlAutopurge} is set.
         *
         * If you set `allowStale:true`, it'll return the stale value *as well as*
         * deleting it. If you don't set this, then it'll return `undefined` when
         * you try to get a stale entry.
         *
         * Note that when a stale entry is fetched, _even if it is returned due to
         * `allowStale` being set_, it is removed from the cache immediately. You
         * can suppress this behavior by setting
         * {@link OptionsBase.noDeleteOnStaleGet}, either in the constructor, or in
         * the options provided to {@link LRUCache#get}.
         *
         * This may be overridden by passing an options object to `cache.get()`.
         * The `cache.has()` method will always return `false` for stale items.
         *
         * Only relevant if a ttl is set.
         */
        allowStale?: boolean;
        /**
         * Function that is called on items when they are dropped from the
         * cache, as `dispose(value, key, reason)`.
         *
         * This can be handy if you want to close file descriptors or do
         * other cleanup tasks when items are no longer stored in the cache.
         *
         * **NOTE**: It is called _before_ the item has been fully removed
         * from the cache, so if you want to put it right back in, you need
         * to wait until the next tick. If you try to add it back in during
         * the `dispose()` function call, it will break things in subtle and
         * weird ways.
         *
         * Unlike several other options, this may _not_ be overridden by
         * passing an option to `set()`, for performance reasons.
         *
         * The `reason` will be one of the following strings, corresponding
         * to the reason for the item's deletion:
         *
         * - `evict` Item was evicted to make space for a new addition
         * - `set` Item was overwritten by a new value
         * - `expire` Item expired its TTL
         * - `fetch` Item was deleted due to a failed or aborted fetch, or a
         *   fetchMethod returning `undefined.
         * - `delete` Item was removed by explicit `cache.delete(key)`,
         *   `cache.clear()`, or `cache.set(key, undefined)`.
         */
        dispose?: Disposer<K, V>;
        /**
         * Function that is called when new items are inserted into the cache,
         * as `onInsert(value, key, reason)`.
         *
         * This can be useful if you need to perform actions when an item is
         * added, such as logging or tracking insertions.
         *
         * Unlike some other options, this may _not_ be overridden by passing
         * an option to `set()`, for performance and consistency reasons.
         */
        onInsert?: Inserter<K, V>;
        /**
         * The same as {@link OptionsBase.dispose}, but called *after* the entry
         * is completely removed and the cache is once again in a clean state.
         *
         * It is safe to add an item right back into the cache at this point.
         * However, note that it is *very* easy to inadvertently create infinite
         * recursion this way.
         */
        disposeAfter?: Disposer<K, V>;
        /**
         * Set to true to suppress calling the
         * {@link OptionsBase.dispose} function if the entry key is
         * still accessible within the cache.
         *
         * This may be overridden by passing an options object to
         * {@link LRUCache#set}.
         *
         * Only relevant if `dispose` or `disposeAfter` are set.
         */
        noDisposeOnSet?: boolean;
        /**
         * Boolean flag to tell the cache to not update the TTL when setting a new
         * value for an existing key (ie, when updating a value rather than
         * inserting a new value).  Note that the TTL value is _always_ set (if
         * provided) when adding a new entry into the cache.
         *
         * Has no effect if a {@link OptionsBase.ttl} is not set.
         *
         * May be passed as an option to {@link LRUCache#set}.
         */
        noUpdateTTL?: boolean;
        /**
         * Set to a positive integer to track the sizes of items added to the
         * cache, and automatically evict items in order to stay below this size.
         * Note that this may result in fewer than `max` items being stored.
         *
         * Attempting to add an item to the cache whose calculated size is greater
         * that this amount will be a no-op. The item will not be cached, and no
         * other items will be evicted.
         *
         * Optional, must be a positive integer if provided.
         *
         * Sets `maxEntrySize` to the same value, unless a different value is
         * provided for `maxEntrySize`.
         *
         * At least one of `max`, `maxSize`, or `TTL` is required. This must be a
         * positive integer if set.
         *
         * Even if size tracking is enabled, **it is strongly recommended to set a
         * `max` to prevent unbounded growth of the cache.**
         *
         * Note also that size tracking can negatively impact performance,
         * though for most cases, only minimally.
         */
        maxSize?: Size;
        /**
         * The maximum allowed size for any single item in the cache.
         *
         * If a larger item is passed to {@link LRUCache#set} or returned by a
         * {@link OptionsBase.fetchMethod} or {@link OptionsBase.memoMethod}, then
         * it will not be stored in the cache.
         *
         * Attempting to add an item whose calculated size is greater than
         * this amount will not cache the item or evict any old items, but
         * WILL delete an existing value if one is already present.
         *
         * Optional, must be a positive integer if provided. Defaults to
         * the value of `maxSize` if provided.
         */
        maxEntrySize?: Size;
        /**
         * A function that returns a number indicating the item's size.
         *
         * Requires {@link OptionsBase.maxSize} to be set.
         *
         * If not provided, and {@link OptionsBase.maxSize} or
         * {@link OptionsBase.maxEntrySize} are set, then all
         * {@link LRUCache#set} calls **must** provide an explicit
         * {@link SetOptions.size} or sizeCalculation param.
         */
        sizeCalculation?: SizeCalculator<K, V>;
        /**
         * Method that provides the implementation for {@link LRUCache#fetch}
         *
         * ```ts
         * fetchMethod(key, staleValue, { signal, options, context })
         * ```
         *
         * If `fetchMethod` is not provided, then `cache.fetch(key)` is equivalent
         * to `Promise.resolve(cache.get(key))`.
         *
         * If at any time, `signal.aborted` is set to `true`, or if the
         * `signal.onabort` method is called, or if it emits an `'abort'` event
         * which you can listen to with `addEventListener`, then that means that
         * the fetch should be abandoned. This may be passed along to async
         * functions aware of AbortController/AbortSignal behavior.
         *
         * The `fetchMethod` should **only** return `undefined` or a Promise
         * resolving to `undefined` if the AbortController signaled an `abort`
         * event. In all other cases, it should return or resolve to a value
         * suitable for adding to the cache.
         *
         * The `options` object is a union of the options that may be provided to
         * `set()` and `get()`. If they are modified, then that will result in
         * modifying the settings to `cache.set()` when the value is resolved, and
         * in the case of
         * {@link OptionsBase.noDeleteOnFetchRejection} and
         * {@link OptionsBase.allowStaleOnFetchRejection}, the handling of
         * `fetchMethod` failures.
         *
         * For example, a DNS cache may update the TTL based on the value returned
         * from a remote DNS server by changing `options.ttl` in the `fetchMethod`.
         */
        fetchMethod?: Fetcher<K, V, FC>;
        /**
         * Method that provides the implementation for {@link LRUCache#memo}
         */
        memoMethod?: Memoizer<K, V, FC>;
        /**
         * Set to true to suppress the deletion of stale data when a
         * {@link OptionsBase.fetchMethod} returns a rejected promise.
         */
        noDeleteOnFetchRejection?: boolean;
        /**
         * Do not delete stale items when they are retrieved with
         * {@link LRUCache#get}.
         *
         * Note that the `get` return value will still be `undefined`
         * unless {@link OptionsBase.allowStale} is true.
         *
         * When using time-expiring entries with `ttl`, by default stale
         * items will be removed from the cache when the key is accessed
         * with `cache.get()`.
         *
         * Setting this option will cause stale items to remain in the cache, until
         * they are explicitly deleted with `cache.delete(key)`, or retrieved with
         * `noDeleteOnStaleGet` set to `false`.
         *
         * This may be overridden by passing an options object to `cache.get()`.
         *
         * Only relevant if a ttl is used.
         */
        noDeleteOnStaleGet?: boolean;
        /**
         * Set to true to allow returning stale data when a
         * {@link OptionsBase.fetchMethod} throws an error or returns a rejected
         * promise.
         *
         * This differs from using {@link OptionsBase.allowStale} in that stale
         * data will ONLY be returned in the case that the {@link LRUCache#fetch}
         * fails, not any other times.
         *
         * If a `fetchMethod` fails, and there is no stale value available, the
         * `fetch()` will resolve to `undefined`. Ie, all `fetchMethod` errors are
         * suppressed.
         *
         * Implies `noDeleteOnFetchRejection`.
         *
         * This may be set in calls to `fetch()`, or defaulted on the constructor,
         * or overridden by modifying the options object in the `fetchMethod`.
         */
        allowStaleOnFetchRejection?: boolean;
        /**
         * Set to true to return a stale value from the cache when the
         * `AbortSignal` passed to the {@link OptionsBase.fetchMethod} dispatches
         * an `'abort'` event, whether user-triggered, or due to internal cache
         * behavior.
         *
         * Unless {@link OptionsBase.ignoreFetchAbort} is also set, the underlying
         * {@link OptionsBase.fetchMethod} will still be considered canceled, and
         * any value it returns will be ignored and not cached.
         *
         * Caveat: since fetches are aborted when a new value is explicitly
         * set in the cache, this can lead to fetch returning a stale value,
         * since that was the fallback value _at the moment the `fetch()` was
         * initiated_, even though the new updated value is now present in
         * the cache.
         *
         * For example:
         *
         * ```ts
         * const cache = new LRUCache<string, any>({
         *   ttl: 100,
         *   fetchMethod: async (url, oldValue, { signal }) =>  {
         *     const res = await fetch(url, { signal })
         *     return await res.json()
         *   }
         * })
         * cache.set('https://example.com/', { some: 'data' })
         * // 100ms go by...
         * const result = cache.fetch('https://example.com/')
         * cache.set('https://example.com/', { other: 'thing' })
         * console.log(await result) // { some: 'data' }
         * console.log(cache.get('https://example.com/')) // { other: 'thing' }
         * ```
         */
        allowStaleOnFetchAbort?: boolean;
        /**
         * Set to true to ignore the `abort` event emitted by the `AbortSignal`
         * object passed to {@link OptionsBase.fetchMethod}, and still cache the
         * resulting resolution value, as long as it is not `undefined`.
         *
         * When used on its own, this means aborted {@link LRUCache#fetch} calls
         * are not immediately resolved or rejected when they are aborted, and
         * instead take the full time to await.
         *
         * When used with {@link OptionsBase.allowStaleOnFetchAbort}, aborted
         * {@link LRUCache#fetch} calls will resolve immediately to their stale
         * cached value or `undefined`, and will continue to process and eventually
         * update the cache when they resolve, as long as the resulting value is
         * not `undefined`, thus supporting a "return stale on timeout while
         * refreshing" mechanism by passing `AbortSignal.timeout(n)` as the signal.
         *
         * For example:
         *
         * ```ts
         * const c = new LRUCache({
         *   ttl: 100,
         *   ignoreFetchAbort: true,
         *   allowStaleOnFetchAbort: true,
         *   fetchMethod: async (key, oldValue, { signal }) => {
         *     // note: do NOT pass the signal to fetch()!
         *     // let's say this fetch can take a long time.
         *     const res = await fetch(`https://slow-backend-server/${key}`)
         *     return await res.json()
         *   },
         * })
         *
         * // this will return the stale value after 100ms, while still
         * // updating in the background for next time.
         * const val = await c.fetch('key', { signal: AbortSignal.timeout(100) })
         * ```
         *
         * **Note**: regardless of this setting, an `abort` event _is still
         * emitted on the `AbortSignal` object_, so may result in invalid results
         * when passed to other underlying APIs that use AbortSignals.
         *
         * This may be overridden in the {@link OptionsBase.fetchMethod} or the
         * call to {@link LRUCache#fetch}.
         */
        ignoreFetchAbort?: boolean;
        /**
         * In some cases, you may want to swap out the performance/Date object
         * used for TTL tracking. This should almost certainly NOT be done in
         * production environments!
         *
         * This value defaults to `global.performance` if it has a `now()` method,
         * or the `global.Date` object otherwise.
         */
        perf?: Perf;
    }
    interface OptionsMaxLimit<K, V, FC> extends OptionsBase<K, V, FC> {
        max: Count;
    }
    interface OptionsTTLLimit<K, V, FC> extends OptionsBase<K, V, FC> {
        ttl: Milliseconds;
        ttlAutopurge: boolean;
    }
    interface OptionsSizeLimit<K, V, FC> extends OptionsBase<K, V, FC> {
        maxSize: Size;
    }
    /**
     * The valid safe options for the {@link LRUCache} constructor
     */
    type Options<K, V, FC> = OptionsMaxLimit<K, V, FC> | OptionsSizeLimit<K, V, FC> | OptionsTTLLimit<K, V, FC>;
    /**
     * Entry objects used by {@link LRUCache#load} and {@link LRUCache#dump},
     * and returned by {@link LRUCache#info}.
     */
    interface Entry<V> {
        value: V;
        ttl?: Milliseconds;
        size?: Size;
        start?: Milliseconds;
    }
}
/**
 * Default export, the thing you're using this module to get.
 *
 * The `K` and `V` types define the key and value types, respectively. The
 * optional `FC` type defines the type of the `context` object passed to
 * `cache.fetch()` and `cache.memo()`.
 *
 * Keys and values **must not** be `null` or `undefined`.
 *
 * All properties from the options object (with the exception of `max`,
 * `maxSize`, `fetchMethod`, `memoMethod`, `dispose` and `disposeAfter`) are
 * added as normal public members. (The listed options are read-only getters.)
 *
 * Changing any of these will alter the defaults for subsequent method calls.
 */
export declare class LRUCache<K extends {}, V extends {}, FC = unknown> {
    #private;
    /**
     * {@link LRUCache.OptionsBase.perf}
     */
    get perf(): Perf;
    /**
     * {@link LRUCache.OptionsBase.ttl}
     */
    ttl: LRUCache.Milliseconds;
    /**
     * {@link LRUCache.OptionsBase.ttlResolution}
     */
    ttlResolution: LRUCache.Milliseconds;
    /**
     * {@link LRUCache.OptionsBase.ttlAutopurge}
     */
    ttlAutopurge: boolean;
    /**
     * {@link LRUCache.OptionsBase.updateAgeOnGet}
     */
    updateAgeOnGet: boolean;
    /**
     * {@link LRUCache.OptionsBase.updateAgeOnHas}
     */
    updateAgeOnHas: boolean;
    /**
     * {@link LRUCache.OptionsBase.allowStale}
     */
    allowStale: boolean;
    /**
     * {@link LRUCache.OptionsBase.noDisposeOnSet}
     */
    noDisposeOnSet: boolean;
    /**
     * {@link LRUCache.OptionsBase.noUpdateTTL}
     */
    noUpdateTTL: boolean;
    /**
     * {@link LRUCache.OptionsBase.maxEntrySize}
     */
    maxEntrySize: LRUCache.Size;
    /**
     * {@link LRUCache.OptionsBase.sizeCalculation}
     */
    sizeCalculation?: LRUCache.SizeCalculator<K, V>;
    /**
     * {@link LRUCache.OptionsBase.noDeleteOnFetchRejection}
     */
    noDeleteOnFetchRejection: boolean;
    /**
     * {@link LRUCache.OptionsBase.noDeleteOnStaleGet}
     */
    noDeleteOnStaleGet: boolean;
    /**
     * {@link LRUCache.OptionsBase.allowStaleOnFetchAbort}
     */
    allowStaleOnFetchAbort: boolean;
    /**
     * {@link LRUCache.OptionsBase.allowStaleOnFetchRejection}
     */
    allowStaleOnFetchRejection: boolean;
    /**
     * {@link LRUCache.OptionsBase.ignoreFetchAbort}
     */
    ignoreFetchAbort: boolean;
    /**
     * Do not call this method unless you need to inspect the
     * inner workings of the cache.  If anything returned by this
     * object is modified in any way, strange breakage may occur.
     *
     * These fields are private for a reason!
     *
     * @internal
     */
    static unsafeExposeInternals<K extends {}, V extends {}, FC extends unknown = unknown>(c: LRUCache<K, V, FC>): {
        starts: ZeroArray | undefined;
        ttls: ZeroArray | undefined;
        autopurgeTimers: (NodeJS.Timeout | undefined)[] | undefined;
        sizes: ZeroArray | undefined;
        keyMap: Map<K, number>;
        keyList: (K | undefined)[];
        valList: (V | BackgroundFetch<V> | undefined)[];
        next: NumberArray;
        prev: NumberArray;
        readonly head: Index;
        readonly tail: Index;
        free: StackLike;
        isBackgroundFetch: (p: unknown) => p is BackgroundFetch<V>;
        backgroundFetch: (k: K, index: number | undefined, options: LRUCache.FetchOptions<K, V, FC>, context: unknown) => BackgroundFetch<V>;
        moveToTail: (index: number) => void;
        indexes: (options?: {
            allowStale: boolean;
        }) => Generator<Index, void, unknown>;
        rindexes: (options?: {
            allowStale: boolean;
        }) => Generator<Index, void, unknown>;
        isStale: (index: number | undefined) => boolean;
    };
    /**
     * {@link LRUCache.OptionsBase.max} (read-only)
     */
    get max(): LRUCache.Count;
    /**
     * {@link LRUCache.OptionsBase.maxSize} (read-only)
     */
    get maxSize(): LRUCache.Count;
    /**
     * The total computed size of items in the cache (read-only)
     */
    get calculatedSize(): LRUCache.Size;
    /**
     * The number of items stored in the cache (read-only)
     */
    get size(): LRUCache.Count;
    /**
     * {@link LRUCache.OptionsBase.fetchMethod} (read-only)
     */
    get fetchMethod(): LRUCache.Fetcher<K, V, FC> | undefined;
    get memoMethod(): LRUCache.Memoizer<K, V, FC> | undefined;
    /**
     * {@link LRUCache.OptionsBase.dispose} (read-only)
     */
    get dispose(): LRUCache.Disposer<K, V> | undefined;
    /**
     * {@link LRUCache.OptionsBase.onInsert} (read-only)
     */
    get onInsert(): LRUCache.Inserter<K, V> | undefined;
    /**
     * {@link LRUCache.OptionsBase.disposeAfter} (read-only)
     */
    get disposeAfter(): LRUCache.Disposer<K, V> | undefined;
    constructor(options: LRUCache.Options<K, V, FC> | LRUCache<K, V, FC>);
    /**
     * Return the number of ms left in the item's TTL. If item is not in cache,
     * returns `0`. Returns `Infinity` if item is in cache without a defined TTL.
     */
    getRemainingTTL(key: K): number;
    /**
     * Return a generator yielding `[key, value]` pairs,
     * in order from most recently used to least recently used.
     */
    entries(): Generator<[K, V], void, unknown>;
    /**
     * Inverse order version of {@link LRUCache.entries}
     *
     * Return a generator yielding `[key, value]` pairs,
     * in order from least recently used to most recently used.
     */
    rentries(): Generator<(K | V)[], void, unknown>;
    /**
     * Return a generator yielding the keys in the cache,
     * in order from most recently used to least recently used.
     */
    keys(): Generator<K, void, unknown>;
    /**
     * Inverse order version of {@link LRUCache.keys}
     *
     * Return a generator yielding the keys in the cache,
     * in order from least recently used to most recently used.
     */
    rkeys(): Generator<K, void, unknown>;
    /**
     * Return a generator yielding the values in the cache,
     * in order from most recently used to least recently used.
     */
    values(): Generator<V, void, unknown>;
    /**
     * Inverse order version of {@link LRUCache.values}
     *
     * Return a generator yielding the values in the cache,
     * in order from least recently used to most recently used.
     */
    rvalues(): Generator<V | undefined, void, unknown>;
    /**
     * Iterating over the cache itself yields the same results as
     * {@link LRUCache.entries}
     */
    [Symbol.iterator](): Generator<[K, V], void, unknown>;
    /**
     * A String value that is used in the creation of the default string
     * description of an object. Called by the built-in method
     * `Object.prototype.toString`.
     */
    [Symbol.toStringTag]: string;
    /**
     * Find a value for which the supplied fn method returns a truthy value,
     * similar to `Array.find()`. fn is called as `fn(value, key, cache)`.
     */
    find(fn: (v: V, k: K, self: LRUCache<K, V, FC>) => boolean, getOptions?: LRUCache.GetOptions<K, V, FC>): V | undefined;
    /**
     * Call the supplied function on each item in the cache, in order from most
     * recently used to least recently used.
     *
     * `fn` is called as `fn(value, key, cache)`.
     *
     * If `thisp` is provided, function will be called in the `this`-context of
     * the provided object, or the cache if no `thisp` object is provided.
     *
     * Does not update age or recenty of use, or iterate over stale values.
     */
    forEach(fn: (v: V, k: K, self: LRUCache<K, V, FC>) => unknown, thisp?: unknown): void;
    /**
     * The same as {@link LRUCache.forEach} but items are iterated over in
     * reverse order.  (ie, less recently used items are iterated over first.)
     */
    rforEach(fn: (v: V, k: K, self: LRUCache<K, V, FC>) => unknown, thisp?: unknown): void;
    /**
     * Delete any stale entries. Returns true if anything was removed,
     * false otherwise.
     */
    purgeStale(): boolean;
    /**
     * Get the extended info about a given entry, to get its value, size, and
     * TTL info simultaneously. Returns `undefined` if the key is not present.
     *
     * Unlike {@link LRUCache#dump}, which is designed to be portable and survive
     * serialization, the `start` value is always the current timestamp, and the
     * `ttl` is a calculated remaining time to live (negative if expired).
     *
     * Always returns stale values, if their info is found in the cache, so be
     * sure to check for expirations (ie, a negative {@link LRUCache.Entry#ttl})
     * if relevant.
     */
    info(key: K): LRUCache.Entry<V> | undefined;
    /**
     * Return an array of [key, {@link LRUCache.Entry}] tuples which can be
     * passed to {@link LRUCache#load}.
     *
     * The `start` fields are calculated relative to a portable `Date.now()`
     * timestamp, even if `performance.now()` is available.
     *
     * Stale entries are always included in the `dump`, even if
     * {@link LRUCache.OptionsBase.allowStale} is false.
     *
     * Note: this returns an actual array, not a generator, so it can be more
     * easily passed around.
     */
    dump(): [K, LRUCache.Entry<V>][];
    /**
     * Reset the cache and load in the items in entries in the order listed.
     *
     * The shape of the resulting cache may be different if the same options are
     * not used in both caches.
     *
     * The `start` fields are assumed to be calculated relative to a portable
     * `Date.now()` timestamp, even if `performance.now()` is available.
     */
    load(arr: [K, LRUCache.Entry<V>][]): void;
    /**
     * Add a value to the cache.
     *
     * Note: if `undefined` is specified as a value, this is an alias for
     * {@link LRUCache#delete}
     *
     * Fields on the {@link LRUCache.SetOptions} options param will override
     * their corresponding values in the constructor options for the scope
     * of this single `set()` operation.
     *
     * If `start` is provided, then that will set the effective start
     * time for the TTL calculation. Note that this must be a previous
     * value of `performance.now()` if supported, or a previous value of
     * `Date.now()` if not.
     *
     * Options object may also include `size`, which will prevent
     * calling the `sizeCalculation` function and just use the specified
     * number if it is a positive integer, and `noDisposeOnSet` which
     * will prevent calling a `dispose` function in the case of
     * overwrites.
     *
     * If the `size` (or return value of `sizeCalculation`) for a given
     * entry is greater than `maxEntrySize`, then the item will not be
     * added to the cache.
     *
     * Will update the recency of the entry.
     *
     * If the value is `undefined`, then this is an alias for
     * `cache.delete(key)`. `undefined` is never stored in the cache.
     */
    set(k: K, v: V | undefined, setOptions?: LRUCache.SetOptions<K, V, FC>): this;
    /**
     * Evict the least recently used item, returning its value or
     * `undefined` if cache is empty.
     */
    pop(): V | undefined;
    /**
     * Check if a key is in the cache, without updating the recency of use.
     * Will return false if the item is stale, even though it is technically
     * in the cache.
     *
     * Check if a key is in the cache, without updating the recency of
     * use. Age is updated if {@link LRUCache.OptionsBase.updateAgeOnHas} is set
     * to `true` in either the options or the constructor.
     *
     * Will return `false` if the item is stale, even though it is technically in
     * the cache. The difference can be determined (if it matters) by using a
     * `status` argument, and inspecting the `has` field.
     *
     * Will not update item age unless
     * {@link LRUCache.OptionsBase.updateAgeOnHas} is set.
     */
    has(k: K, hasOptions?: LRUCache.HasOptions<K, V, FC>): boolean;
    /**
     * Like {@link LRUCache#get} but doesn't update recency or delete stale
     * items.
     *
     * Returns `undefined` if the item is stale, unless
     * {@link LRUCache.OptionsBase.allowStale} is set.
     */
    peek(k: K, peekOptions?: LRUCache.PeekOptions<K, V, FC>): V | undefined;
    /**
     * Make an asynchronous cached fetch using the
     * {@link LRUCache.OptionsBase.fetchMethod} function.
     *
     * If the value is in the cache and not stale, then the returned
     * Promise resolves to the value.
     *
     * If not in the cache, or beyond its TTL staleness, then
     * `fetchMethod(key, staleValue, { options, signal, context })` is
     * called, and the value returned will be added to the cache once
     * resolved.
     *
     * If called with `allowStale`, and an asynchronous fetch is
     * currently in progress to reload a stale value, then the former
     * stale value will be returned.
     *
     * If called with `forceRefresh`, then the cached item will be
     * re-fetched, even if it is not stale. However, if `allowStale` is also
     * set, then the old value will still be returned. This is useful
     * in cases where you want to force a reload of a cached value. If
     * a background fetch is already in progress, then `forceRefresh`
     * has no effect.
     *
     * If multiple fetches for the same key are issued, then they will all be
     * coalesced into a single call to fetchMethod.
     *
     * Note that this means that handling options such as
     * {@link LRUCache.OptionsBase.allowStaleOnFetchAbort},
     * {@link LRUCache.FetchOptions.signal},
     * and {@link LRUCache.OptionsBase.allowStaleOnFetchRejection} will be
     * determined by the FIRST fetch() call for a given key.
     *
     * This is a known (fixable) shortcoming which will be addresed on when
     * someone complains about it, as the fix would involve added complexity and
     * may not be worth the costs for this edge case.
     *
     * If {@link LRUCache.OptionsBase.fetchMethod} is not specified, then this is
     * effectively an alias for `Promise.resolve(cache.get(key))`.
     *
     * When the fetch method resolves to a value, if the fetch has not
     * been aborted due to deletion, eviction, or being overwritten,
     * then it is added to the cache using the options provided.
     *
     * If the key is evicted or deleted before the `fetchMethod`
     * resolves, then the AbortSignal passed to the `fetchMethod` will
     * receive an `abort` event, and the promise returned by `fetch()`
     * will reject with the reason for the abort.
     *
     * If a `signal` is passed to the `fetch()` call, then aborting the
     * signal will abort the fetch and cause the `fetch()` promise to
     * reject with the reason provided.
     *
     * **Setting `context`**
     *
     * If an `FC` type is set to a type other than `unknown`, `void`, or
     * `undefined` in the {@link LRUCache} constructor, then all
     * calls to `cache.fetch()` _must_ provide a `context` option. If
     * set to `undefined` or `void`, then calls to fetch _must not_
     * provide a `context` option.
     *
     * The `context` param allows you to provide arbitrary data that
     * might be relevant in the course of fetching the data. It is only
     * relevant for the course of a single `fetch()` operation, and
     * discarded afterwards.
     *
     * **Note: `fetch()` calls are inflight-unique**
     *
     * If you call `fetch()` multiple times with the same key value,
     * then every call after the first will resolve on the same
     * promise<sup>1</sup>,
     * _even if they have different settings that would otherwise change
     * the behavior of the fetch_, such as `noDeleteOnFetchRejection`
     * or `ignoreFetchAbort`.
     *
     * In most cases, this is not a problem (in fact, only fetching
     * something once is what you probably want, if you're caching in
     * the first place). If you are changing the fetch() options
     * dramatically between runs, there's a good chance that you might
     * be trying to fit divergent semantics into a single object, and
     * would be better off with multiple cache instances.
     *
     * **1**: Ie, they're not the "same Promise", but they resolve at
     * the same time, because they're both waiting on the same
     * underlying fetchMethod response.
     */
    fetch(k: K, fetchOptions: unknown extends FC ? LRUCache.FetchOptions<K, V, FC> : FC extends undefined | void ? LRUCache.FetchOptionsNoContext<K, V> : LRUCache.FetchOptionsWithContext<K, V, FC>): Promise<undefined | V>;
    fetch(k: unknown extends FC ? K : FC extends undefined | void ? K : never, fetchOptions?: unknown extends FC ? LRUCache.FetchOptions<K, V, FC> : FC extends undefined | void ? LRUCache.FetchOptionsNoContext<K, V> : never): Promise<undefined | V>;
    /**
     * In some cases, `cache.fetch()` may resolve to `undefined`, either because
     * a {@link LRUCache.OptionsBase#fetchMethod} was not provided (turning
     * `cache.fetch(k)` into just an async wrapper around `cache.get(k)`) or
     * because `ignoreFetchAbort` was specified (either to the constructor or
     * in the {@link LRUCache.FetchOptions}). Also, the
     * {@link LRUCache.OptionsBase.fetchMethod} may return `undefined` or `void`, making
     * the test even more complicated.
     *
     * Because inferring the cases where `undefined` might be returned are so
     * cumbersome, but testing for `undefined` can also be annoying, this method
     * can be used, which will reject if `this.fetch()` resolves to undefined.
     */
    forceFetch(k: K, fetchOptions: unknown extends FC ? LRUCache.FetchOptions<K, V, FC> : FC extends undefined | void ? LRUCache.FetchOptionsNoContext<K, V> : LRUCache.FetchOptionsWithContext<K, V, FC>): Promise<V>;
    forceFetch(k: unknown extends FC ? K : FC extends undefined | void ? K : never, fetchOptions?: unknown extends FC ? LRUCache.FetchOptions<K, V, FC> : FC extends undefined | void ? LRUCache.FetchOptionsNoContext<K, V> : never): Promise<V>;
    /**
     * If the key is found in the cache, then this is equivalent to
     * {@link LRUCache#get}. If not, in the cache, then calculate the value using
     * the {@link LRUCache.OptionsBase.memoMethod}, and add it to the cache.
     *
     * If an `FC` type is set to a type other than `unknown`, `void`, or
     * `undefined` in the LRUCache constructor, then all calls to `cache.memo()`
     * _must_ provide a `context` option. If set to `undefined` or `void`, then
     * calls to memo _must not_ provide a `context` option.
     *
     * The `context` param allows you to provide arbitrary data that might be
     * relevant in the course of fetching the data. It is only relevant for the
     * course of a single `memo()` operation, and discarded afterwards.
     */
    memo(k: K, memoOptions: unknown extends FC ? LRUCache.MemoOptions<K, V, FC> : FC extends undefined | void ? LRUCache.MemoOptionsNoContext<K, V> : LRUCache.MemoOptionsWithContext<K, V, FC>): V;
    memo(k: unknown extends FC ? K : FC extends undefined | void ? K : never, memoOptions?: unknown extends FC ? LRUCache.MemoOptions<K, V, FC> : FC extends undefined | void ? LRUCache.MemoOptionsNoContext<K, V> : never): V;
    /**
     * Return a value from the cache. Will update the recency of the cache
     * entry found.
     *
     * If the key is not found, get() will return `undefined`.
     */
    get(k: K, getOptions?: LRUCache.GetOptions<K, V, FC>): V | undefined;
    /**
     * Deletes a key out of the cache.
     *
     * Returns true if the key was deleted, false otherwise.
     */
    delete(k: K): boolean;
    /**
     * Clear the cache entirely, throwing away all values.
     */
    clear(): void;
}
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