How to assign same type as one of the type member?

November 28, 2023

For example, I have this code:

interface DbType {
    id: string,
}

interface RowType extends DbType {
    name: string
}

class db<T> { // How do I put that it must be an extension of DbType?

    insert(item: T) { }
    delete(id: [typeof id]) { } // What should I put here?
}

I want to limit the parameter type, also the T type, to be corresponds to DbType.

So when I do new db<RowType>() I want the delete method would accept the same type as DbType.id

How to do that?

>Solution :

I think what you’re looking for is a simple generic constraint and an Indexed Access type for the delete parameter.

interface DbType {
  id: string;
}

interface RowType extends DbType {
  name: string;
}

class DB<T extends DbType> {
  insert(item: T) {}
  delete(id: T["id"]) {} 
}

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