# redux-sac

Slice and compose redux-type reducers.

## `subReducer(key, reducer, additionalKey, ...)`

Creates a wrapper reducer that call `reducer`
on the substate specified by `key`.
You may use dot notation.
Rest of the state is left untouched.

```js
	const r = subReducer("persons", personReducer);

    r({persons: ["John", "Jill"], cars: ["Honda"]}, action);
    // => {
    //   persons: personReducer(["John", "Jill"], action), 
    //   cars: ["Honda"]
    // }
```

Respects redux convention that if no change was made,
the identical object should be returned. So in previous case,
if `personReducer` would return the identical array,
`r` would return the state object it was passed in.

If persons were deeper in hierarchy, it could have been created as
`const r = subReducer("files.persons", personReducer);` for example.

You may pass additional keys (also with possible dot-notation)
as addition arguments. In that case, additional parts of state
will be fetched and passed to a sub-reducer:

```js
	const r = subReducer("persons", personReducer, "assets.cars");

    r({persons: ["John", "Jill"], assets: {cars: ["Honda"]}}, action);
    // => {
    //   persons: personReducer(["John", "Jill"], action, ["Honda"]), 
    //   assets: {cars: ["Honda"]}
    // }
```

This technique is mentioned in Redux docs, in "Beyond combineReducers" page.