CDI spec statement about Typecasting

[chasetec]

Section 2.2.3. Typecasting between bean types from the final spec implies that given:

public class BizImp implements Biz {}

The following two lines would be valid:

@Inject Biz iRef;
@Inject BizImp cRef;

But that in the client I could not latter do a:

BizImp ref = (BizImp)iRef;

I only see this typecasting limitation in the final spec and not in the Weld docs. It actually works in Weld and in fact the spec says might result in an exception at runtime.

This seems like such an arbitrary and silly limitation that is bound to cause problems porting applications across CDI implementations. What is the reasoning behind this constraint?

[nickarls]

Well, there could be other classes that implements Biz (enabled @Alternatives in other scenarios).

[chasetec]

Right, but the spec statement doesn't say that the casting error might be caused by a AmbiguousResolutionException. It seems to leave the possibility that a CDI implementation may generate contextual references that don't extend the bean implementation class.