getCache = associatedObjectForCache => {
		const entry = cache.get(associatedObjectForCache);
		if (entry !== undefined) return entry;
		/** @type {Map<string, T>} */
		const map = new Map();
		cache.set(associatedObjectForCache, map);
		return map;
	}
@param {AssociatedObjectForCache} associatedObjectForCache an object to which the cache will be attached
@returns {CacheItem<T>} cache item