Function discriminated

test/typescript/dispatch.ts:22–46

* Dispatch accepts type argument that restricts allowed action types.

()

 * Dispatch accepts type argument that restricts allowed action types.
 */
function discriminated() {
  interface IncrementAction {
    type: 'INCREMENT'
    count?: number
  }

  interface DecrementAction {
    type: 'DECREMENT'
    count?: number
  }

  // Union of all actions in the app.
  type MyAction = IncrementAction | DecrementAction

  const dispatch: Dispatch<MyAction> = null as any

  dispatch({ type: 'INCREMENT' })
  dispatch({ type: 'DECREMENT', count: 10 })
  // Known actions are strictly checked.
  // @ts-expect-error
  dispatch({ type: 'DECREMENT', count: '' })
  // Unknown actions are rejected.
  // @ts-expect-error
  dispatch({ type: 'SOME_OTHER_TYPE' })
}