Unchecked conversion and super raw type

[Maurizio Cimadamore]

The spec is saying:

"The method m is applicable by subtyping if and only if both of the 
following conditions hold:

For 1 ≤ i ≤ n, either:

Ai <: Si (§4.10), or

Ai is convertible to some type Ci by unchecked conversion (§5.1.9), and 
Ci <: Si."


And I agree this seems to be a spec problem - there's no unchecked 
conversion for going from B to A<String>, as unchecked conversion 
requires that source bases type and target nbae type are the same - in 
this case we have that B != A so no unchecked conversion applies.

However, javac (and Eclipse) implement a relaxed check; for example, 
javac is happy whenever it can find a supertype of the LHS type that 
matches the base type of the RHS. Which in this case is satisfied.

Maurizio


On 11/04/13 23:40, Zhong Yu wrote:
>
>
>
> On Thu, Apr 11, 2013 at 5:10 PM, Zhong Yu <zhong.j.yu at gmail.com 
> <mailto:zhong.j.yu at gmail.com>> wrote:
>
>     Consider this example:
>
>     public class Test
>     {
>         static class A<T> {}
>
>         static class B extends A {}
>
>         void foo(A<String> a) {}
>
>         void foo(B b) {}
>
>         void test()
>         {
>             B b = new B();
>             foo(b); // error: reference to foo is ambiguous
>         }
>     }
>
>     For the method invocation expression `foo(b)`, method `foo(B)` is
>     applicable by subtyping. However is that also true for
>     `foo(A<String>)`? By the letter of the spec, we cannot find a Ci
>     such that "B" is convertible to Ci by unchecked conversion and Ci
>     <: A<String>. So my understanding is that `foo(A<String>)` is not
>     applicable to `foo(b)` by subtyping, and the code should compile
>     since only one applicable method is found during "15.12.2.2. Phase 1"
>
>
>
> Or, is this a bug of the spec? Maybe the spec intends to say
>
> For 1 ≤ /i/ ≤ /n/, either:
>
>  *
>
>     A_i |<:| S_i (§4.10
>     <http://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.10>),
>     or
>
>  *
>
>     A_i |<:| |S_i |
>
> The second clause is for the legacy code that saw a non-generic method 
> parameter type.
>
> Zhong Yu
>

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