An object whose values correspond to different reducer
functions that need to be combined into one. One handy way to obtain it
is to use import * as reducers syntax. The reducers may never
return undefined for any action. Instead, they should return their
initial state if the state passed to them was undefined, and the current
state for any unrecognized action.
A reducer function that invokes every reducer inside the passed object, and builds a state object with the same shape.
Turns an object whose values are different reducer functions, into a single reducer function. It will call every child reducer, and gather their results into a single state object, whose keys correspond to the keys of the passed reducer functions.