Is it possible for sibling functions to have the same generic type in common?

Let's consider the functions setup and retrieve:

function setup<Data = any>() {
  // ...
}

function retrieve<Data = any>(): Data { 
  return 1 as Data
} 

If we execute the setup function:

type Item = {name: 'example'}

setup<Item>() 

I am interested in automatically inferring the return type of the retrieve function to be the same as the input type for the setup function.

const result = retrieve()
// Desired outcome: the type of result is inferred as `Item` 

I have a feeling this might not be achievable. One possible solution could involve having the setup function return something of type S, which can then be passed to the retrieve function. Are there any other approaches to tackle this issue?

Answer №1

Your functions seem to have no connection. It's as if they could belong in completely different modules altogether.

If you desire them to work together, consider grouping them within a class...

class SomeClass<Schema> {
  init() {
    // ...
  }

  query(): Schema {
    return 1 as Schema;
  }
}

const instance = new SomeClass<Foo>();
instance.init();
const res = instance.query();

or opt for a factory function instead

function factory <Schema>() {
  return {
    init() {
      // ...
    },
    query(): Schema {
      return 1 as Schema;
    }
  };
}

const { init, query } = factory<Foo>();

Answer №2

Regrettably, it is not possible for two closely related functions to have the same generic parameter. The static type checker is unable to infer this information.

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