Provide a way for map to initialize its schema

[zxch3n]

Commonly, a map container has a schema. There is no way to initialize the schema in the current version. It's fine if the values of the entries are JSON values. But it may be problematic if the value is a Container.

Consider the following example.

struct TodoList {
    todos: List
}

Users may initialize the todos field concurrently and insert a to-do item concurrently. However, in the current implementation, one user's edits will override the other's and thus only have a to-do item in the list.

The current workaround in the application code is to initialize all fields immediately after creating the map. But by using this approach, there is still potential data loss when the schema is changed.

Solution

We may need alias of container to support this feature. i.e., there may exist two different ids that point to the same container.

[zxch3n]

It's too complex. Users can initialize those fields before syncing the container to avoid concurrent edits.