Exception transparency

[Maurizio Cimadamore]

On 09/06/10 12:37, Rémi Forax wrote:
> Le 09/06/2010 12:06, Maurizio Cimadamore a écrit :
>    
>> On 09/06/10 09:23, Maurizio Cimadamore wrote:
>>
>>      
>>> On 09/06/10 00:44, Neal Gafter wrote:
>>>
>>>
>>>        
>>>>>     Function<throws IOException>     e = #(IOException e){...};
>>>>>
>>>>>
>>>>>            
>>> Hi
>>> just to be clear, on which basis would you reject the above statement? I
>>> guess your argument is that a lambda accepting an argument  of type E
>>> cannot be SAM-converted to an interface whose method accepts an argument
>>> of type 'throws E' (and, more generally, that E and 'throws E' are not
>>> interchangeable). Am I reading correctly?
>>>
>>>
>>>        
>> To be clearer, what I mean is, given the following declarations:
>>
>> class Foo<throws E>   { ... }
>>
>> Foo<throws MyException>   foo1 = ... //1
>> Foo<MyException>   foo2 = ... //2
>> foo1 = foo2; //3
>>
>> *) What is the type parameter of Foo in (1) ? A disjunctive type having
>> one component (of type MyException)? Or a straight type-parameter (non
>> disjunctive) of type MyException?
>>
>> *) is (2) allowed? If so what is the semantics? Does the singleton type
>> MyException get converted into a disjunctive type having just one
>> component (of type MyException)?
>>
>> *) is (3) allowed? If so, depending on the semantics you choose for (1)
>> and (2), aren't we (indirectly perhaps) already supporting a form of
>> 'covariance', as we assume that C<E>   <: C<throws E>   because E<: throws
>> E ? If so, what are the consequences of these subtyping rule?
>>
>> Maurizio
>>
>>      
> you can also add:
>
> Foo<? extends throws MyException>  foo3 = ...
> and
> Foo<throws ? extends MyException>  foo4 = ...
>    
Uhmm - I don't think the first is legal; it's like '? extends ? extends 
String'; I think that the argument of a wildcard should be a *type* and 
not another type-argument. Of course, the same objection could (in 
principle) be applied to 'throws'.

Maurizio
> And please remember that use-site variance (i.e ? extends/super) is
> something that is not easy to grasp,
> only few of my students understand it correctly. Declaration site
> variance seems easier.
>
> Rémi
>
>