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Inheritance and type narrowing prevent private member access in base class. #11454
Description
TypeScript Version: 2.0.3
Code
class Animal {
private sound: string;
public makeSound() {
if (this instanceof Cat || this instanceof Dog) {
this.sound = "grr"; // Errors
}
}
}
class Cat extends Animal {
public walk() {}
}
class Dog extends Animal {
public eat() {}
}Expected behavior:
Should be able to access private member in its declaring class.
Actual behavior:
Cannot access private member in its declaring class if the subclasses have different members and we narrow the type of this to a union type of its subclasses.
Activity
falsandtru commentedon Oct 9, 2016
I think
thisnarrowed by subclasses should have external accessibility of them. So I think this is a correct behavior.normalser commentedon Oct 9, 2016
I think it should work. Works in Java. https://goo.gl/Pb5p2Y
mhegazy commentedon Dec 14, 2016
So we should narrow to
Cat & Animal | Dog & Animal?jakebailey commentedon Jul 6, 2023
Just looking at old bugs; this one was fixed in 3.9+ via #38277, though I'm not sure that the PR actually introduces a test for this particular case (though the underlying thing is in fact the same;
thisis narrowed to(this & Cat) | (this & Dog)).