constructor(items) {
		/**
		 * @private
		 * @type {TupleSet<T, V>}
		 */
		this._set = new TupleSet(items);
		/**
		 * @private
		 * @type {Iterator<[T, V, ...EXPECTED_ANY]>}
		 */
		this._iterator = this._set[Symbol.iterator]();
	}
@param {Iterable<[T, V, ...EXPECTED_ANY]>=} items The initial elements.