TypeScript Generic sub type

Question

Is that possible to pass a namespace as a generic and later access types from the namespace? I would like to achieve something like that:

namespace Test {
  export type A = { ... }
  export type B = { ... }
}

type Gen<T> = (a: T.A, b: T.B) => void;

// using Gen<T>
let x: Gen<Test>;

No, you can't do that. But maybe you can elaborate on why you would like to do that to begin with? What's your real scenario? — Nitzan Tomer
– Nitzan Tomer, Commented Feb 7, 2017 at 13:13
I am building an app using Angular2 and Apollo. I am using a gql-gen to generate types. It generates a namespaces per query, and inside it adds Result and Variables types. I would like to use those in my generic type which uses both Result and Variables and was hoping to do Cast<UpvotePostMutation> instead of Cast<UpvotePostMutation.Result, UpvotePostMutation.Variables>. Too bad it's not possible, but thanks for clarifying :). — Dracco
– Dracco, Commented Feb 7, 2017 at 13:19

Nitzan Tomer · Accepted Answer · 2017-02-07 14:13:55Z

1

I'm not exactly sure that I understand you, but if I do, then how about this:

namespace Test {
    export const Result = {
        num: 3
    }

    export const Variables = {
        str: "string"
    }
}

interface MyNamespace<R, V> {
    Result: R;
    Variables: V;
}

function Gen<R, V>(namespace: MyNamespace<R, V>): void {}

Gen(Test);

(code in playground)

Edit

You can do something similar with the query function you want:

function query<R, V>(namespace: MyNamespace<R, V>, data: { query: any, variables?: V }): Array<R> {
    return [];    
}

// type of arr is { num: number; }[]
let arr = query(Test, { query: "query", variables: { str: "" } });

(code in playground)

edited Feb 7, 2017 at 14:13

answered Feb 7, 2017 at 13:35

Nitzan Tomer

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3 Comments

Dracco Over a year ago

Not exactly what I needed. I wanted to use it like query(data: {query: any, variables?: Variables}): ApolloQueryObservable<Result>; so Variables and Result are separate.

Dracco Over a year ago

Yea, but this is still passing both R and V generics :P. I was hoping to pass just their container and "unpack" them inside ;).

Nitzan Tomer Over a year ago

You are not "passing" any generics, the compiler infers that on its' own based on the "container" namespace.

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