More Typing Problems

[Neal Gafter]

On Tuesday, September 7, 2010, Maurizio Cimadamore
<maurizio.cimadamore at oracle.com> wrote:
> On 07/09/10 14:55, Florian Weimer wrote:
>> * Maurizio Cimadamore:
>>
>>
>>> with an actual argument of the kind:
>>>
>>> #(c){c.getName()}
>>>
>>>
>>> So, given that there's no explicit type on 'c' and given that the method
>>> 'select' is accepting *any* subtype of SAM<T,U>  for any U, I'm having
>>> hard times in imagining an inference scheme that can infer something
>>> meaningful (not Object) for 'c'.
>>>
>> This particular case isn't really a problem.  OCaml infers its type as
>>
>>    <  getName : 'a; ..>  ->  'a
>>
>> meaning "a function from an object which has got a getName method (and
>> possibly other methods) returning a value of type 'a to a value of
>> type 'a".  There are probably some issues if you treat SAM conversion
>> as a variant of ML type ascription, but those can probably be solved.
>>
> Smells of structural subtyping ;-) ?

Indeed, generics with wildcards is structural subtyping.  The problem
is that SAMs can't be generic (i.e. have the abstract method be
generic), which excludes the ML solution.