javac rejects valid java 7 code

[Zhong Yu]

In Java7, shouldn't S be inferred to A2<? extends Number&...> instead?
Then, the return type of `foo(x,y)` goes through capture conversion
and becomes A2<CAP#> which can be fed to baz().

On Tue, Nov 19, 2013 at 7:01 AM, Vicente-Arturo Romero-Zaldivar
<vicente.romero at oracle.com> wrote:
> Hi Anna,
>
> I don't think that this is a bug. This is what javac is inferring for
> your original example:
>
> var S
>      upper bounds = A2<S1>,java.lang.Object
>      lower bounds = A2<java.lang.Integer>,A2<java.lang.Long>
>      eq bounds = []
>
> var S1
>      upper bounds = java.lang.Object
>      lower bounds = []
>      eq bounds = java.lang.Long,java.lang.Integer
>
> all types of the form Type1, Type2 are intersection types and were
> introduced to create more correct and strict inference restrictions. In
> java7 they would have been inferred as Object, and that's why the
> example works in 7. So what javac8 is saying is that it can't find a
> solution for these variables with the given restrictions. Note that if
> in your example method bar is for example defined as:
>
> void bar(A2<Integer> y, A2<Integer> x) {...}
>
> then the example will compile in 8 as now it's possible to find a
> solution. The inference in that case will look like:
>
> var S
>      upper bounds = A2<S1>,java.lang.Object
>      lower bounds = A2<java.lang.Integer>
>      eq bounds = []
> var S1
>      upper bounds = java.lang.Object
>      lower bounds = []
>      eq bounds = java.lang.Integer
>
> As you can see the introduction of intersection types to model bounds
> makes the compiler both smarter and stricter.
>
> I will continue checking the rest of the examples.
>
> Thanks,
> Vicente.
>
>
> On 18/11/13 15:31, Anna Kozlova wrote:
>> Hi,
>>
>>
>>
>> This code compiles with java 1.7 (also 1.6) but fails to compile with 1.8
>> (b. 115)
>>
>>
>>
>> abstract class A2<T>{
>>
>>      abstract <S> S foo(S x, S y);
>>
>>      abstract <S1> void baz(A2<S1> a)
>>
>>
>>
>>      void bar(A2<Integer> y, A2<Long> x){
>>
>>           baz(foo(x, y));
>>
>>      }
>>
>> }
>>
>>
>>
>> java: method baz in class A2<T> cannot be applied to given types;
>>
>>    required: A2<S1>
>>
>>    found: A2<capture#1 of ? extends java.lang.Number&java.lang.Comparable<?
>> extends java.lang.Number&java.lang.Comparable<?>>>
>>
>>    reason: inferred type does not conform to equality constraint(s)
>>
>>      inferred: java.lang.Long
>>
>>      equality constraints(s): java.lang.Long,java.lang.Integer
>>
>>
>>
>> Are these equality constraint really for S1? How does javac get them
>> independently from whom they belong?
>>
>>
>>
>> Thanks,
>>
>> Anna
>>
>>
>
>