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Dynamic Super Types #11967
Description
Now, that #11929 is PR landed. I would really love to have some syntax to specify an arbitrary super type of T. This can be especially helpful in creating strongly typed ORM database frameworks.
Proposal
If K is constrained to be a key of T i.e K extends keyof T. Then the syntax:
{ ...K: ...T[K] }
Means spread the keys K and values of T in {}.
Example
Here is an example usage of an envisioned ORM framework:
interface IUser {
id: string;
name: string;
email: string;
createdAt: string;
updatedAt: string;
password: string;
// ...
}
interface Options<T, K extends keyof T> {
attributes: T[K][];
}
interface Model<IInstance> {
findOne<K extends keyof IInstance>(options: Options<IInstance, K>): { ...K: ...IInstance[K] };
}
declare namespace DbContext {
define<T>(): Model<T>;
}
const Users = DbContext.define<IUser>({
id: { type: DbContext.STRING(50), allowNull: false },
// ...
});
const user = Users.findOne({
attributes: ['id', 'email', 'name'],
where: {
id: 1,
}
});
user.id // no error
user.email // no error
user.name // no error
user.password // error
user.createdAt // error
user.updatedAt // error
Activity
HerringtonDarkholme commentedon Nov 1, 2016
I wonder whether it is doable after #11929 landed. We can use overload + tuple syntax to mock it.
Something like
If we have variadic kinds in #5453, maybe dynamic super type can be supported directly?
Also,
K extends keyof Tseems to stand for one single string literal type to me. But in the return type it is used as a variadic kinds. May be...K extends keyof Tis better?tinganho commentedon Nov 1, 2016
I stumbled upon this too. Though this problem might be a bit hard to solve perfectly.