function Provider({ store, context, children }) {
  const contextValue = useMemo(() => {
    const subscription = new Subscription(store)
    subscription.onStateChange = subscription.notifyNestedSubs
    return {
      store,
      subscription
    }
  }, [store])

  const previousState = useMemo(() => store.getState(), [store])

  useEffect(() => {
    const { subscription } = contextValue
    subscription.trySubscribe()

    if (previousState !== store.getState()) {
      subscription.notifyNestedSubs()
    }
    return () => {
      subscription.tryUnsubscribe()
      subscription.onStateChange = null
    }
  }, [contextValue, previousState])

export default class Subscription {
  constructor(store, parentSub) {
    this.store = store
    this.parentSub = parentSub
    this.unsubscribe = null
    this.listeners = nullListeners

    this.handleChangeWrapper = this.handleChangeWrapper.bind(this)
  }

  trySubscribe() {
    if (!this.unsubscribe) {
      this.unsubscribe = this.parentSub
        ? this.parentSub.addNestedSub(this.handleChangeWrapper)
        : this.store.subscribe(this.handleChangeWrapper)

      this.listeners = createListenerCollection()
    }
  }

  handleChangeWrapper() {
    if (this.onStateChange) {
      this.onStateChange()
    }
  }

  notifyNestedSubs() {
    this.listeners.notify()
  }

      const [subscription, notifyNestedSubs] = useMemo(() => {
        if (!shouldHandleStateChanges) return NO_SUBSCRIPTION_ARRAY

        // This Subscription's source should match where store came from: props vs. context. A component
        // connected to the store via props shouldn't use subscription from context, or vice versa.
        const subscription = new Subscription(
          store,
          didStoreComeFromProps ? null : contextValue.subscription
        )

        // `notifyNestedSubs` is duplicated to handle the case where the component is unmounted in
        // the middle of the notification loop, where `subscription` will then be null. This can
        // probably be avoided if Subscription's listeners logic is changed to not call listeners
        // that have been unsubscribed in the  middle of the notification loop.
        const notifyNestedSubs = subscription.notifyNestedSubs.bind(
          subscription
        )

        return [subscription, notifyNestedSubs]
      }, [store, didStoreComeFromProps, contextValue])

      // Our re-subscribe logic only runs when the store/subscription setup changes
      useIsomorphicLayoutEffectWithArgs(
        subscribeUpdates,
        [
          shouldHandleStateChanges,
          store,
          subscription,
          childPropsSelector,
          lastWrapperProps,
          lastChildProps,
          renderIsScheduled,
          childPropsFromStoreUpdate,
          notifyNestedSubs,
          forceComponentUpdateDispatch
        ],
        [store, subscription, childPropsSelector]
      )

function subscribeUpdates(
  // 省略。上の配列に入ってるものが渡されてきます
) {
  // 省略

  // We'll run this callback every time a store subscription update propagates to this component
  const checkForUpdates = () => {
    // 後で見ます
  }

  // Actually subscribe to the nearest connected ancestor (or store)
  subscription.onStateChange = checkForUpdates
  subscription.trySubscribe()

  // 省略
}

  trySubscribe() {
    if (!this.unsubscribe) {
      this.unsubscribe = this.parentSub
        ? this.parentSub.addNestedSub(this.handleChangeWrapper)
        : this.store.subscribe(this.handleChangeWrapper)

      this.listeners = createListenerCollection()
    }
  }

  // We'll run this callback every time a store subscription update propagates to this component
  const checkForUpdates = () => {
    if (didUnsubscribe) {
      // Don't run stale listeners.
      // Redux doesn't guarantee unsubscriptions happen until next dispatch.
      return
    }

    const latestStoreState = store.getState()

    let newChildProps, error
    try {
      // Actually run the selector with the most recent store state and wrapper props
      // to determine what the child props should be
      newChildProps = childPropsSelector(
        latestStoreState,
        lastWrapperProps.current
      )
    } catch (e) {
      error = e
      lastThrownError = e
    }

    if (!error) {
      lastThrownError = null
    }

    // If the child props haven't changed, nothing to do here - cascade the subscription update
    if (newChildProps === lastChildProps.current) {
      if (!renderIsScheduled.current) {
        notifyNestedSubs()
      }
    } else {
      // Save references to the new child props.  Note that we track the "child props from store update"
      // as a ref instead of a useState/useReducer because we need a way to determine if that value has
      // been processed.  If this went into useState/useReducer, we couldn't clear out the value without
      // forcing another re-render, which we don't want.
      lastChildProps.current = newChildProps
      childPropsFromStoreUpdate.current = newChildProps
      renderIsScheduled.current = true

      // If the child props _did_ change (or we caught an error), this wrapper component needs to re-render
      forceComponentUpdateDispatch({
        type: 'STORE_UPDATED',
        payload: {
          error
        }
      })
    }
  }

      // Set up refs to coordinate values between the subscription effect and the render logic
      const lastChildProps = useRef()
      const lastWrapperProps = useRef(wrapperProps)
      const childPropsFromStoreUpdate = useRef()
      const renderIsScheduled = useRef(false)

      // We need to force this wrapper component to re-render whenever a Redux store update
      // causes a change to the calculated child component props (or we caught an error in mapState)
      const [
        [previousStateUpdateResult],
        forceComponentUpdateDispatch
      ] = useReducer(storeStateUpdatesReducer, EMPTY_ARRAY, initStateUpdates)