Abstract Constructor Assignability Not Restricted Enough

[aozgaa]

Consider the following code snippet:

abstract class A {}
class B extends A {}

var A2: new () => A;
var BCtor: typeof B;

A2 = A;
BCtor = A1;

The first assignment should fail because A2 is new-able (it isn't an abstract constructor type), but no error is reported.

EDIT: simplified the sample.

[tinganho]

If this is a bug how do I do this #2947 (comment)?

@RyanCavanaugh I have another question about abstract classes. I wonder how I define a function that accepts a derived abstract class that is not abstract and the function should also "new" it.

The following doesn't work:

function testDerived<T extends typeof ComposerComponent>(DerivedClass: T) {
   new DerivedClass(); // error
}
function testDerived(DerivedClass: typeof ComposerComponent) {
   new DerivedClass(); // error
}

And @RyanCavanaugh suggested:

function testDerived(DerivedClass: new() => ComposerComponent) {

I think that there should be a modifier for declaring derivative of an abstract class that is not abstract.

var A2: new () => implementationof A;

[aozgaa]

Let me check my understanding. Suppose our class hierarchy looks like

    A
   / \
  B   C 

where A is abstract but B,C are not.

Then you want to have an object AA which has a type that allows

AA = B;
AA = C;
new AA;

but forbids

AA = A;

If my understanding is correct, that's precisely the capability that should be provided by
var A2: new () => A; in the example above. Right now, the forbidden condition isn't forbidden.

If I'm misunderstanding, can you clarify where I'm going astray?

[tinganho]

If my understanding is correct, that's precisely the capability that should be provided by
var A2: new () => A; in the example above. Right now, the forbidden condition isn't forbidden.

This is the only way that I know of that can do the capability we are talking about.

Though personally I also feel that this is a bug. Though I want to have the capability to declare a non abstract class declaration type. If you fix this bug, then I don't know how to do it(except using any).

[aozgaa]

Could you clarify what you mean by "a non abstract class declaration type"?

[tinganho]

@aozgaa don't know the real name of it. but just to clarify my meaning:

abstract class A {}
typeof A // abstract class declaration type
class B extends A {}
typeof B //non-abstract class declaration type

[aozgaa]

I see. So what's missing from the constructor function type A2 above? Do you want to also have the static-side of A encoded into A2? What's an example of a use-case of the "non-abstract class declaration types" when dealing with abstract classes?

[tinganho]

Do you want to also have the static-side of A encoded into A2

I think this is already handled?

What's an example of a use-case of the "non-abstract class declaration types" when dealing with abstract classes

As I mentioned in the quoted comments above. I want pass a "non-abstract class declaration type" to a function and instantiate using new.

[aozgaa]

@tinganho

Today, the following code will work:

        class A {}

        function factory(AA: typeof A) {
            return new AA;
        }

[tinganho]

@aozgaa thanks!