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Deriving from object and intersection types problem #13732
Description
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> { }
Activity
mhegazy commentedon Jan 30, 2017
the
Tis unknown. it would have been fine to extend from_A<{}>, but not fromT. The reason is the compiler does not know whatTis at the declaration site, and thus does not know how to check theextendsrelationship in the interface declaration.consider using intersection types, as:
tamayika commentedon Jan 30, 2017
OK, thanks!!