docs: simplify and clarify advanced createAction examples

README.md

@@ -111,18 +111,18 @@ The action creator function will be typed to take whatever you provide as a
 payload type.
 
 If your action creator needs to take arguments other than whatever your payload
-is typed as you can provide types in the generic signature:
+is typed as you can simply provide a typed payload creator function:
 
 ```ts
-// a, b, and c are inferred below:
-const addThreeNumbers = createAction<number, [number, number, number]>('ADD_THREE_NUMBERS', (a, b, c) => a + b + c);
+// addThreeNumbers accepts three ordinal number aguments and has a number payload:
+const addThreeNumbers = createAction('ADD_THREE_NUMBERS', (a: number, b: number, c: number) => a + b + c);
 ```
 
 If you need to customize the [SFP] `meta` property you can supply a second meta
-customizer function:
+creator function:
 
 ```ts
-const addThreeNumbers = createAction<number, [number, number, number], number>(
+const addThreeNumbers = createAction<number, [number, number, number], string>(
   'ADD_THREE_NUMBERS',
   // Create `payload`
   (a, b, c) => a + b + c,
@@ -131,6 +131,11 @@ const addThreeNumbers = createAction<number, [number, number, number], number>(
 );
 ```
 
+Note that the payload and meta creators must accept the same arguments, but can
+return different types. In the example above the payload creator takes three
+numbers and returns a number while the meta creator takes three numbers and
+returns a string.
+
 ### `handleAction(actionCreator, (state: Draft<State>, payload) => void, initialState?: State)`
 
 The `handleAction` function returns a single reducer function. The first

src/create-action.test.ts

@@ -63,6 +63,31 @@ test('meta customizer', () => {
   });
 });
 
+test('generic inference', () => {
+  const ac = createAction('generic-inference', (a: number, b: number, c: number) => a + b + c);
+  expect(ac.type).toBe('generic-inference');
+  expect(ac(1, 2, 3)).toEqual({
+    type: 'generic-inference',
+    payload: 6,
+  });
+});
+
+test('generic inference with meta', () => {
+  const ac = createAction<number, [number, number, number], string>(
+    'generic-inference-with-meta',
+    // Create `payload`
+    (a, b, c) => a + b + c,
+    // Create `meta`
+    (a, b, c) => `${a} + ${b} + ${c}`,
+  );
+  expect(ac.type).toBe('generic-inference-with-meta');
+  expect(ac(1, 2, 3)).toEqual({
+    type: 'generic-inference-with-meta',
+    payload: 6,
+    meta: '1 + 2 + 3',
+  });
+});
+
 test('error payload', () => {
   const ac = createAction<Error>('with-error');
   expect(ac.type).toBe('with-error');