Trouble inferring type of lambda

[Howard Lovatt]

Hi Mauritzio,

I think it is a bug, like I said in the original post the 'return
type' is 'NeverReturns' not void, which should be assignable to
anything (including Integer). Scala and BGGA handle this case, they
both have a 'NeverReturns' type (Scala and BGGA Nothing).

Cheers,

 -- Howard.

On 23 August 2010 20:35, Maurizio Cimadamore
<maurizio.cimadamore at oracle.com> wrote:
> This is not a bug. You are trying to SAM convert the following lambda:
>
> #(x) { throws Exception(); }
>
> into the following target method:
>
> <throws E> Integer call( Integer a1 ) throws E
>
> This is not possible, since the lambda expression is inferred to yield
> 'void' (no return expression found), while the target method returns
> Integer.
>
> Maurizio
>
>
>
> On 22/08/10 18:45, maurizio cimadamore wrote:
>>
>> On 22/08/2010 07:09, Howard Lovatt wrote:
>>
>>>
>>> For:
>>>
>>>    public interface Method1<R, A1, throws E>   { public R call( A1 a1 )
>>> throws E; }
>>>
>>> and:
>>>
>>>    public<throws E>   void forEach( final Method1<Integer, Integer, E>
>>> method ) throws E { ... }
>>>
>>> The compiler has trouble with:
>>>
>>>     il.forEach( #( i ) { throw new Exception(); } ); // Need to catch
>>> checked exception
>>>
>>> Giving:
>>>
>>> lambdas/Main.java:34: method forEach in class IntList11 cannot be
>>> applied to given types
>>>        il.forEach( #( i ) { throw new Exception(); } ); // Need to
>>> catch checked exception
>>>          ^
>>>    required: Method1<Integer,Integer,E>
>>>    found: #void(?)(Exception)
>>>    where E is a type-variable:
>>>      E extends Exception declared in method
>>> <E>forEach(Method1<Integer,Integer,E>)
>>>
>>> Qualifying doesn't help:
>>>
>>>    Method1<Integer, Integer, Exception>   #( i ) { throw new Exception();
>>> }
>>>
>>> It gives:
>>>
>>> lambdas/Main.java:34: incompatible types; no instance(s) of type
>>> variable(s) ? exist so that #void(?)(Exception) conforms to
>>> Method1<Integer,Integer,Exception>
>>>        il.forEach( Method1<Integer, Integer, Exception>   #( i ) { throw
>>> new Exception(); } ); // Need to catch checked exception
>>>                    ^
>>>    required: Method1<Integer,Integer,Exception>
>>>    found:    #void(?)(Exception)
>>>
>>> Is the problem that the return type isn't expressible? It isn't really
>>> void, it is 'NeverReturns'.
>>>
>>>
>>
>> Uhmm the problem here seems more related with a failure in inference of
>> the lambda parameter (the '?' that you are seeing). Again it would be
>> helpful to see the declaration of the receiver class as well as the type
>> of 'il'.
>>
>> Maurizio
>>
>>>
>>>    -- Howard.
>>>
>>>
>>>
>>
>>
>
>



-- 
  -- Howard.