PR #2467 breaks TS interface inheritance

[lukescott]

Do you want to request a feature or report a bug?

Bug

export default mapHandlers<SingleChoice>({
	select(state, {value}: SelectAction) {
		return input(state, value)
	},

	reset(state) {
		return input(state, "")
	},

	validate(state) {
		return input(state, state.value)
	},

import {Action, Reducer} from "redux"

export type HandlerMapObject<S> = {
	[name: string]: Reducer<S>
}

export default
function mapHandlers<S>(
	handlers: HandlerMapObject<S>,
	defaultReducer?: Reducer<S>
): Reducer<S> {
	return (state, action) => {
		const reducer = handlers[action.type] || defaultReducer
		if (reducer !== undefined) {
			return reducer(state, action)
		}
		return state
	}
}

What is the current behavior?

Argument of type '{ select(state: SingleChoice, { value }: SelectAction): SingleChoice; reset(state: SingleChoice):...' is not assignable to parameter of type 'HandlerMapObject<SingleChoice>'. Property 'select' is incompatible with index signature. Type '(state: SingleChoice, { value }: SelectAction) => SingleChoice' is not assignable to type 'Reducer<SingleChoice>'. Types of parameters '__1' and 'action' are incompatible. Type 'AnyAction' is not assignable to type 'SelectAction'. Property 'value' is missing in type 'AnyAction'.

What is the expected behavior?

No errors.

Which versions of Redux, and which browser and OS are affected by this issue? Did this work in previous versions of Redux?

master - error
3.7.1 - works

This was caused by PR #2467

[lukescott]

Looks like the reason for the change was there was an issue w/ <A extends Action> part, but this works:

export type Reducer<S> = (state: S, action: Action) => S

[timdorr]

What version of TS are you using?

[lukescott]

@timdorr 2.4.1. Sorry, I had some information incorrect. I updated the original issue.

[lukescott]

Gah, sorry. I actually got it to work with AnyAction. I broke something while trying to debug the original issue I was having, which was related to the TypeScript version.

Either of these work as well though:

export type Reducer<S> = (state: S, action: Action) => S

export type Reducer<S, A extends Action = Action> = (state: S, action: Action) => S