Deriving from object and intersection types problem

[tamayika]

TypeScript Version: nightly (2.2.0-dev.20170128)

Code

interface Person{
  name: string;
}

interface A<T> {

}

type _A<T> = A<T> & T;

interface B<T> extends _A<T> { }

type TypedPerson = B<Person>;

Expected behavior:
no error
Actual behavior:
line interface B<T> extends _A<T> { } is error // TS2312: An interface may only extend a class or another interface.

Now, we can deriving from object and intersection types by #13604.
But this is only for _A<T> is statically composed of object or intersection types.
I think we can solve this problem if we can delay type evaluation until actual type resolution at the line type TypedPerson = B<Person>;
or, we need generics type restriction like below?

interface B<T is interface> extends _A<T> { }

[mhegazy]

the T is unknown. it would have been fine to extend from _A<{}>, but not from T. The reason is the compiler does not know what T is at the declaration site, and thus does not know how to check the extends relationship in the interface declaration.

consider using intersection types, as:

type B<T> = _A<T> & { <other declarations> };

[tamayika]

OK, thanks!!