Request for review: proposal for @FunctionalInterface checking

[Doug Lea]

On 01/02/13 15:29, Joe Darcy wrote:

>> Perhaps @FunctionalInterface can be extended to provide this. Instead of just
>>
>> @FunctionalInterface
>> interface Predicate<T> { ... }
>>
>> the annotation could capture the parameter and return types as well:
>>
>> @FunctionalInterface(return = boolean.class,
>>                      params = { Object.class })
>> interface Predicate<T> { ... }
>>
>> (or better, some scheme that lets us encode generic signatures rather than
>> erased ones).
>
> Hmmm.  I think trying to use an annotation in this way would be very awkward and
> error prone since we'd  basically be asking people to generate an (erased?)
> signature by hand.
>
> -Joe
>
>>
>> Then we're making a clear statement that "Predicate<T> is a functional
>> interface with type signature T->boolean", which would open the door to future
>> loosenings in a less ad-hoc way?
>>
>> Doug, does this help at all?
>>

I thought it was a cute parlor trick that might tide us over until there
are proper function types, and would be OK as such unless people like Joe
complained, which he did :-)

-Doug