Factory closure constructor inferring type act like "not sure" or "confused"

[renjithspace]

Bug Report

🔎 Search Terms

closure, infer

🕗 Version & Regression Information

• I think this is a generic issue, not a specific version related

💻 Code

// Example 1

class Car {
  speed = 45;
}

/**
 * Vehicle factory constructor
 * 
 * This Vehicle constructor simply return
 * and instance of Car.
 */
class Vehicle {
  speed = 35;

  constructor() {
    return new Car();
  }
}

const vehicle = new Vehicle(); // Inferring as instance of `Vehicle` instead of `Car`, why?

console.log(vehicle.speed); // 45
// If `vehicle` is an instance of `Vehicle` the `vehicle.speed` should return 35, right?

// Example 2

type VehicleType = "car" | "motorcycle";

class Car {
  speed = 35;
}

class Motorcycle {
  speed = 45;
}

class Vehicle {
  static construct(type: VehicleType) {
    switch (type) {
      case "car":
        return new Car();
      case "motorcycle":
        return new Motorcycle();
      default:
        throw new Error("Invalid vehicle type");
    }
  }
}

const vehicle = Vehicle.construct("car"); //Inferring as `Car` | `Motorcycle`, why not just `Car`?
console.log(vehicle.speed); // 35

// There's no confusion for runtime,
// it clearly identifies vehicle is a car and returns its `speed` correctly
// Is this a weakness of inferring types in typescript?

🙁 Actual behavior

In both examples, the Vehicle instance is not inferring the correct type that matches the runtime behavior.

🙂 Expected behavior

In both examples, the Vehicle instance infers the correct type that matches the runtime behavior.

[IllusionMH]

Looks related to or duplicate of #38519, #11588 etc.

[MartinJohns]

And regarding example 2: Nothing in the functions type signature it indicates that the argument "car" will always return a Car. TypeScript does not go and analyze the logic within the function to determine the return type.

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.