Properties of instances of anonymous classes have type <any> after an instanceof guard.

TypeScript Version: 2.4.1

Code

function create_my_class<T>() {
    return class {
        value: T;
        constructor(
            value: T
        ) {
            this.value = value;
        }
    }
}
const MyClassWithNumber = create_my_class<number>();
const with_number = new MyClassWithNumber(234);

with_number.value = 10;
// with_number.value = "sdf"; // error, and rightly so

const something: any = with_number;

if(something instanceof MyClassWithNumber) {
    something.value = 20;
    something.value = "sdf"; // not an error, but should be one
}

Expected behavior:
The last assignment should be marked as a type error by TS.

Actual behavior:
The last assignment is not marked as error. This is somewhat surprising, as the line

with_number.value = "sdf";

is righteously reported as a type error by TS.

Not a huge issue, but prevented me from using a class factory.

Comienza con la reproducción de TypeScript proporcionada y sigue cómo la comprobación de instanceof restringe el valor devuelto por la fábrica de clases genérica. Verifica el comportamiento usando las asignaciones mostradas y, después, asegúrate de que la asignación protegida de tipo String se marque como un error de tipo, mientras que la asignación numérica siga siendo válida.