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Simplify applyMiddleware #3570

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Simplify applyMiddleware #3570

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53 changes: 16 additions & 37 deletions src/applyMiddleware.ts
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Original file line number Diff line number Diff line change
@@ -1,8 +1,10 @@
import compose from './compose'
import { Middleware, MiddlewareAPI } from './types/middleware'
import { AnyAction } from './types/actions'
import { StoreEnhancer, StoreCreator, Dispatch } from './types/store'
import { Reducer } from './types/reducers'
import {
Dispatch,
StoreEnhancer,
StoreEnhancerStoreCreator
} from './types/store'

/**
* Creates a store enhancer that applies middleware to the dispatch method
Expand All @@ -23,40 +25,17 @@ import { Reducer } from './types/reducers'
* @template Ext Dispatch signature added by a middleware.
* @template S The type of the state supported by a middleware.
*/
export default function applyMiddleware(): StoreEnhancer
export default function applyMiddleware<Ext1, S>(
middleware1: Middleware<Ext1, S, any>
): StoreEnhancer<{ dispatch: Ext1 }>
export default function applyMiddleware<Ext1, Ext2, S>(
middleware1: Middleware<Ext1, S, any>,
middleware2: Middleware<Ext2, S, any>
): StoreEnhancer<{ dispatch: Ext1 & Ext2 }>
export default function applyMiddleware<Ext1, Ext2, Ext3, S>(
middleware1: Middleware<Ext1, S, any>,
middleware2: Middleware<Ext2, S, any>,
middleware3: Middleware<Ext3, S, any>
): StoreEnhancer<{ dispatch: Ext1 & Ext2 & Ext3 }>
export default function applyMiddleware<Ext1, Ext2, Ext3, Ext4, S>(
middleware1: Middleware<Ext1, S, any>,
middleware2: Middleware<Ext2, S, any>,
middleware3: Middleware<Ext3, S, any>,
middleware4: Middleware<Ext4, S, any>
): StoreEnhancer<{ dispatch: Ext1 & Ext2 & Ext3 & Ext4 }>
export default function applyMiddleware<Ext1, Ext2, Ext3, Ext4, Ext5, S>(
middleware1: Middleware<Ext1, S, any>,
middleware2: Middleware<Ext2, S, any>,
middleware3: Middleware<Ext3, S, any>,
middleware4: Middleware<Ext4, S, any>,
middleware5: Middleware<Ext5, S, any>
): StoreEnhancer<{ dispatch: Ext1 & Ext2 & Ext3 & Ext4 & Ext5 }>
export default function applyMiddleware<Ext, S = any>(
...middlewares: Middleware<any, S, any>[]
): StoreEnhancer<{ dispatch: Ext }>
export default function applyMiddleware(
...middlewares: Middleware[]
): StoreEnhancer<any> {
return (createStore: StoreCreator) => <S, A extends AnyAction>(
reducer: Reducer<S, A>,
export default function applyMiddleware<
S = any,
M extends Middleware = Middleware
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Why does this need to be generic? In what case would our middleware not be a Middleware? Either we don't need this, or we need to add a test for this generic.

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@jednano jednano Sep 9, 2019 •
edited
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If it's not generic, I can't infer off of it; rather, I do get errors if I try to do typeof middlewares extends Middleware<any, any, infer D>.

Type '(createStore: StoreEnhancerStoreCreator<any, never>) => <S = any, A extends Action<any> = AnyAction>(reducer: Reducer<S, A>, ...args: any[]) => any' is not assignable to type 'StoreEnhancer<never, S>'.
  Type '<S = any, A extends Action<any> = AnyAction>(reducer: Reducer<S, A>, ...args: any[]) => any' is not assignable to type 'StoreEnhancerStoreCreator<never, S>'.
    Type 'any' is not assignable to type 'never'.ts(2322)

It will always be a Middleware, which is why I said it must extend Middleware, but there's no reason someone can't create an interface which extends Middleware and use that too.

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@jednano jednano Sep 9, 2019 •
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Also, we already have tests against this generic in the existing applyMiddleware.spec.ts which pass just fine with npm run test:cov for some reason; though, I am seeing red underlines in my editor (even before my changes here). I've fixed those red-line errors in other pieces of my work, but once I started breaking things apart, it's a bit harder to compose these things into smaller chunks w/o some overlap.

>(
...middlewares: M[]
): StoreEnhancer<
M extends Middleware<any, any, infer D> ? { dispatch: D } : never,
S
> {
return (createStore: StoreEnhancerStoreCreator<any>) => (
reducer,
...args: any[]
) => {
const store = createStore(reducer, ...args)
Expand Down