Class UniqueValueMultiKeyMap

packages/core/src/render3/list_reconciliation.ts:409–475

 * values (in the entire collection) are unique.
 */
export class UniqueValueMultiKeyMap<K, V> {
  // A map from a key to the first value corresponding to this key.
  private kvMap = new Map<K, V>();
  // A map that acts as a linked list of values - each value maps to the next value in this "linked
  // list" (this only works if values are unique). Allocated lazily to avoid memory consumption when
  // there are no duplicated values.
  private _vMap: Map<V, V> | undefined = undefined;

  has(key: K): boolean {
    return this.kvMap.has(key);
  }

  delete(key: K): boolean {
    if (!this.has(key)) return false;

    const value = this.kvMap.get(key)!;
    if (this._vMap !== undefined && this._vMap.has(value)) {
      this.kvMap.set(key, this._vMap.get(value)!);
      this._vMap.delete(value);
    } else {
      this.kvMap.delete(key);
    }

    return true;
  }

  get(key: K): V | undefined {
    return this.kvMap.get(key);
  }

  set(key: K, value: V): void {
    if (this.kvMap.has(key)) {
      let prevValue = this.kvMap.get(key)!;

      // Note: we don't use `assertNotSame`, because the value needs to be stringified even if
      // there is no error which can freeze the browser for large values (see #58509).
      if (ngDevMode && prevValue === value) {
        throw new Error(`Detected a duplicated value ${value} for the key ${key}`);
      }

      if (this._vMap === undefined) {
        this._vMap = new Map();
      }

      const vMap = this._vMap;
      while (vMap.has(prevValue)) {
        prevValue = vMap.get(prevValue)!;
      }
      vMap.set(prevValue, value);
    } else {
      this.kvMap.set(key, value);
    }
  }

  forEach(cb: (v: V, k: K) => void) {
    for (let [key, value] of this.kvMap) {
      cb(value, key);
      if (this._vMap !== undefined) {