Type equality for values

[Maurizio Cimadamore]

On 01/08/14 11:23, Maurizio Cimadamore wrote:
> Right - I would expect that to already be working (modulo the fact 
> that I have not really tested integration of 'any' with value types 
> that much - yet).
Let me backtrack a bit - currently the spec (15.21.3) demands that the 
equality should be accepted if one type is castable to the other. I 
believe in all the examples I've seen so far, that's the case, as there 
is always a chance that the type-variable will be instantiated with the 
same type, so the cast must be allowed.

Maurizio
>
> Maurizio
>
> On 01/08/14 11:07, Brian Goetz wrote:
>> Certainly if we cannot prove T=U then I think this equality 
>> comparison makes no sense.  But if we have
>>
>>    <any T> boolean foo(A<T> a, A<T> b) { return a==b; }
>>
>> this does make sense (assuming we are comparing values for state 
>> equality via ==).
>>
>>
>> On Aug 1, 2014, at 10:10 AM, Paul Govereau <paul.govereau at oracle.com> 
>> wrote:
>>
>>> The following code is valid for reference types:
>>>
>>> class A<T> {
>>>     int x = 0;
>>>
>>>     <T,U> boolean foo(A<T> a, A<U> b) {
>>>         return (a == b);
>>>     }
>>> }
>>>
>>> However, I don't think this makes sense for value types. In the case 
>>> of reference types, the "top" is a realizable type, namely Object; 
>>> but, for values the "top" is not realizable?
>>>
>>> final __ByValue class A<T> {
>>>     final int x = 0;
>>>
>>>     <any T, any U> boolean foo(A<T> a, A<U> b) {
>>>         return (a == b);  // <<--- type error ??
>>>     }
>>> }
>>>
>>> Should this be a type error?
>>>
>>> Paul
>