1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
|
type Action<T, P> = P extends void ? { type : T } : { type: T, payload: P }
enum ActionType {
Foo,
Bar,
Baz,
Batch
}
type ReducerAction =
| Action<ActionType.Bar, number>
| Action<ActionType.Baz, boolean>
| Action<ActionType.Foo, string>
| Action<ActionType.Batch, ReducerAction[]>
function assertNever(a: never): never {
throw new Error("Unreachable!");
}
function reducer(action: ReducerAction): void {
switch(action.type) {
case ActionType.Bar:
const x: number = action.payload;
break;
case ActionType.Baz:
const y: boolean = action.payload;
break;
case ActionType.Foo:
const z: string = action.payload;
break;
case ActionType.Batch:
action.payload.map(reducer);
break;
default: return assertNever(action);
}
}
|
