_peek(thing) {
		if (isWeakKey(thing)) {
			if ((this.f & 4) !== 4) return;
			return /** @type {WeakMap<ArrayElement<K>, WeakTupleMap<K, V>>} */ (
				this.w
			).get(thing);
		}
		if ((this.f & 2) !== 2) return;
		return /** @type {Map<ArrayElement<K>, WeakTupleMap<K, V>>} */ (this.m).get(
			thing
		);
	}
@param {ArrayElement<K>} thing thing
@returns {WeakTupleMap<K, V> | undefined} thing
@private