Recursive Types

A folder can contain other folders, and each of those can contain more folders. A reply to a comment can have its own replies in the same way. To describe data like this, a type must refer to itself, and such a type is called a recursive type.

Here is a comment thread, where each reply is another comment.

type ThreadComment = {
    text: string;
    replies?: ThreadComment[];
};

The replies property uses the type that is being defined. The compiler accepts this because it does not need to expand the type completely. It looks at the inner `ThreadComment