Proposal: Support draft function return value with modified draft

[unadlib]

Regarding return values, Mutative has the same behavior as Immer.

An draft function returned a new value and modified its draft. Either return a new value or modify the draft.

For example,

  expect(() => {
    const state = create({ a: 1 }, (draft) => {
      draft.a = 2;
      return {
        ...draft,
      };
    });
  }).toThrowError();

However, there is an irrational aspect to this approach. As long as a modified draft can be finalized, it should be allowed to return any value.

Therefore, we are considering allowing Mutative to support draft functions returning any value.

[unadlib]

Here are some examples, such as updating an array (filter out items where the name is not 'Test', and set the 'done' value to true for each of the remaining items):

const todoList = [{ name: 'Test' }, { name: 'Learn' }, { name: 'Test' }];
// This will throw the error
const state = create(todoList, (draft) =>
  draft.filter((item) => {
    if (item.name === 'Test') {
      item.done = true;
      return true;
    }
  })
);

We have to write the array update in a similar way.

const todoList = [{ name: 'Test' }, { name: 'Learn' }, { name: 'Test' }];
const state = create(todoList, (draft) => {
  const length = draft.length;
  draft.forEach((item) => {
    if (item.name !== 'Test') return;
    item.done = true;
    draft.push(item);
  });
  draft.splice(0, length);
});

---

There may also be implicit returns.

// If this feature is supported, it means that such implicit returns with will not throw an error.
const state = create({ a: { b: 1 } }, (draft) => draft.a.b = 2);