前端小白，在学redux，想看下createStore实现，发现写法有点看不懂，有好人帮忙解释下吗
以下为

//看不懂的代码块start
export interface StoreCreator {
  <S, A extends Action, Ext, StateExt>(
    reducer: Reducer<S, A>,
    enhancer?: StoreEnhancer<Ext, StateExt>
  ): Store<S & StateExt, A> & Ext
  <S, A extends Action, Ext, StateExt>(
    reducer: Reducer<S, A>,
    preloadedState?: DeepPartial<S>,
    enhancer?: StoreEnhancer<Ext>
  ): Store<S & StateExt, A> & Ext
}

export const createStore: StoreCreator
//看不懂的代码块end

最后一句 是导出 接口类型为StoreCreator 的常量 createStore 的意思吗？
为什么我在外部调用 createStore(param)，这里createStore表现的像是一个function。具体调用处代码：

import { createStore } from 'redux';
import combineReducers from './reducers';

let store = createStore(combineReducers);
export default store;