Trouble inferring type of lambda

[Maurizio Cimadamore]

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.
>>
>>
>>      
>
>