overload resolution with deep nested lambda

[anna.kozlova at jetbrains.com]

Thank you, Maurizio

On 11.09.2014 19:05, Maurizio Cimadamore wrote:
> I think the latest version of the compiler (JDK 9) has been fixed -
> it now gives this:
>
> /home/maurizio/Desktop/Main.java:6: error: incompatible types: cannot
> infer type-variable(s) O
>         List<Optional<Function<String, String>>> list =
> asList(of((String s) -> identity(s)));
>                                                               ^
>     (argument mismatch; Object is not a functional interface)
>   where O is a type-variable:
>     O extends Object declared in method <O>of(O)
>
>
> The message is a bit cryptic - but the compiler now obviously chooses
> asList(Optional), hence the target-type for the lambda is just Object
> (since Optional is raw).
>
> Maurizio
>
> On 11/09/14 15:26, anna.kozlova at jetbrains.com wrote:
>> the part "A method is applicable if it is either applicable by 
>> subtyping (§15.12.2.2), applicable by method invocation conversion 
>> (§15.12.2.3), or it is an applicable variable arity method 
>> (§15.12.2.4)." is from JLS 7, JLS 8 doesn't say so anymore.
>>
>> I believe that (String s) -> identity(s) is not pertinent to 
>> applicability because it is passed to the parameter with type T 
>> (15.12.2.2) so it should not participate in invocation applicability 
>> inference (18.5.1).
>>
>> Thank you
>> Anna
>>
>> On 11.09.2014 17:56, Davin McCall wrote:
>>> On 10/09/14 19:26, anna.kozlova at jetbrains.com wrote:
>>>>
>>>> Because of((String s) -> identity(s)) is potentially compatible 
>>>> with both methods (15.12.2.1), method applicability search yields 2 
>>>> methods applicable by strict invocation, of which asList(Optional a) 
>>>> is more specific (according to 18.5.4) but javac obviously chooses 
>>>> asList(T).
>>>>
>>>> Could someone explain what have I missed here please?
>>>
>>> I'm no expert here, but I believe that 15.12.2.1 identifies
>>> _potentially) applicable methods, which are then filtered according 
>>> to
>>> 15.12.2.2, 15.12.2.3 and 15.12.2.4.
>>>
>>> From 15.12.2: "A method is applicable if it is either applicable by
>>> subtyping (§15.12.2.2), applicable by method invocation conversion
>>> (§15.12.2.3), or it is an applicable variable arity method
>>> (§15.12.2.4)."
>>>
>>> This removes the possibility of using asList(Optional), because no
>>> suitable type can be inferred for O. The only remaining option is
>>> asList(T).
>>>
>>> Davin
>>>
>>>
>>>
>>>
>>
>
>
> !DSPAM:35,5411bb7297752060050014!