webpack/lib/util/StackedCacheMap.js

Packs CommonJs/AMD modules for the browser. Allows to split your codebase into multiple bundles, which can be loaded on demand. Support loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/

"use strict";

/**
 * @template K
 * @template V
 */
class StackedCacheMap {
	constructor() {
		/** @type {Map<K, V>} */
		this.map = new Map();
		/** @type {ReadonlyMap<K, V>[]} */
		this.stack = [];
	}

	/**
	 * @param {ReadonlyMap<K, V>} map map to add
	 * @param {boolean} immutable if 'map' is immutable and StackedCacheMap can keep referencing it
	 */
	addAll(map, immutable) {
		if (immutable) {
			this.stack.push(map);

			// largest map should go first
			for (let i = this.stack.length - 1; i > 0; i--) {
				const beforeLast = this.stack[i - 1];
				if (beforeLast.size >= map.size) break;
				this.stack[i] = beforeLast;
				this.stack[i - 1] = map;
			}
		} else {
			for (const [key, value] of map) {
				this.map.set(key, value);
			}
		}
	}

	/**
	 * @param {K} item the key of the element to add
	 * @param {V} value the value of the element to add
	 * @returns {void}
	 */
	set(item, value) {
		this.map.set(item, value);
	}

	/**
	 * @param {K} item the item to delete
	 * @returns {void}
	 */
	delete(item) {
		throw new Error("Items can't be deleted from a StackedCacheMap");
	}

	/**
	 * @param {K} item the item to test
	 * @returns {boolean} true if the item exists in this set
	 */
	has(item) {
		throw new Error(
			"Checking StackedCacheMap.has before reading is inefficient, use StackedCacheMap.get and check for undefined"
		);
	}

	/**
	 * @param {K} item the key of the element to return
	 * @returns {V} the value of the element
	 */
	get(item) {
		for (const map of this.stack) {
			const value = map.get(item);
			if (value !== undefined) return value;
		}
		return this.map.get(item);
	}

	clear() {
		this.stack.length = 0;
		this.map.clear();
	}

	get size() {
		let size = this.map.size;
		for (const map of this.stack) {
			size += map.size;
		}
		return size;
	}

	[Symbol.iterator]() {
		const iterators = this.stack.map(map => map[Symbol.iterator]());
		let current = this.map[Symbol.iterator]();
		return {
			next() {
				let result = current.next();
				while (result.done && iterators.length > 0) {
					current = iterators.pop();
					result = current.next();
				}
				return result;
			}
		};
	}
}

module.exports = StackedCacheMap;