"Chained" qualified instance creation expressions (diamond in qualifiers)

[Srikanth]

I'll wait for Dan to chime in with chapter and verse, but I believe the 
specification does not
mandate/require/sanction/allow a qualified instance creation expression 
to propagate
the target type or any part thereof to any enclosing instance creation 
expression (qualified
or otherwise).

Srikanth


On Wednesday 06 May 2015 07:36 PM, Georgiy Rakov wrote:
> Hello,
>
> let's consider following example:
>
>     classD {}
>
>     classOuter2<Q> {
>          classOuter1<W> {
>              classFoo<T> { }
>          }
>     }
>
>     public classTest69 {
>
>          public static voidtest(String argv[]) {
>              Outer2<?superD>.Outer1<?superD>.Foo<?superD> f20 =newOuter2<>().newOuter1<>().newFoo<>() {
>                  privateOuter2<Object>.Outer1<Object>.Foo<D> simpleMethod1() {return this; }//compiles Ok
>                  //private Outer2<D>.Outer1<D>.Foo<D> simpleMethod2() { return this; } //causes compilation error
>              };
>          }
>     }
>
>
> JDK9b60 causes Q and W to be inferred as Object. This can be seen:
> - from the fact that code above compiles successfully;
> - from the fact that uncommenting the method above causes compilation 
> failure.
>
> So what we actually have is:
> - Q is inferred as Object;
> - W is inferred as Object;
> - T is inferred as D.
>
> However according to intuition it seems that Q and W should have been 
> inferred as D as it happens to T.
>
> I believe this corresponds to spec, the reasons presented below seem 
> to cause this:
>
> 1. Following assertion from JLS 18.5.2 is not applied when JLS 15.9.3 
> is applied to new Outer2<>() and new Outer1<>():
>
>     Otherwise, the constraint formula ‹Rθ→T› is reduced and
>     incorporated with B_2 .
>
> So for outer classes inference proceeds with no constraint formula 
> actually causing inference variable in question to be inferred as D.
>
> 2. JLS 15.9.3 doesn't use type parameters from outer classes when 
> processing new Foo<>(). Namely following assertion from JLS 15.9.3 
> doesn't mention type parameters from possible outer classes:
>
>     Let F_1 ...F_p be the type parameters of C, and let G_1 ...G_q be
>     the type parameters (if any) of |c_j |.
>
> So constraint formula created by JLS 18.5.2 assertion presented above 
> engages just inference variable from Foo, i. e. T.
>
> However I believe more broad change of spec will be required to 
> implement this "intuition" than just modifying spec according to two 
> points above.
>
> So:
> 1. Could you please tell if I understand correctly that the fact that 
> Q is inferred as Object, W is inferred as Object really corresponds to 
> spec and it's not a JDK issue.
> 2. As for me it looks reasonable to enhance specification so that Q 
> and W would be inferred as D too. Could you please tell if you agree. 
> If you do would it be worth creating spec enhancement in Jira?
>
> Thanks,
> Georgiy.

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