Trivial SAM convertion

[Boaz Nahum]

Thanks for the detailed explanation.



On Tue, Apr 2, 2013 at 4:22 PM, Brian Goetz <brian.goetz at oracle.com> wrote:

> During my attempts to *lambdafying* my code, I came to places like this:
>>
>>
>> *Predicate<File> isDir = File::isDirectory;*
>> **
>> *
>> *
>> *Predicate<File> isFile = isDir.negate();*
>> **
>>
>> *
>>            FileFilter isFileFilter = isFile::test;
>>
>> *
>> *At first, naively I just wrote:
>> *
>> *FileFilter isFileFilter = isFile;
>>
>> *
>> *After realizing my mistake, I wondered 'Why not *?' If we have two SAM
>>
>> interfaces with identical signatures (test & accept) then one can be
>> converted to other.
>>
>
> Yes, the EG discussed the issue of "SAM to SAM conversion" at length. The
> deciding factor was that an existing language feature already gives you
> most of what you want:
>
>   FilterFilter isFileFilter = isFile::test;
>
> Going farther did not seem worthwhile.  The alternatives were:
>  - a special syntax for the conversion
>  - a silent magic conversion
>
> Given that the above is not syntactically awful, and nicely explicit,
> prudence dictated that we stop there.
>
>
>  If I may, one more question. Is this will be ever a valid code ?:
>>
>> Predicate<File> isFile = (File::isDirectory).negate();
>>
>
> Doing so would require unbounded type analysis.  To solve this, the
> compiler would have to say: "What are the instantiations of types that have
> a negate() method that returns Predicate<File>, and, if there's exactly
> one, can I use that as a target type for File::isDirectory?" Seems a lot to
> ask the compiler.
>
>