"it"? "#"? ""?

[Matthew Adams]

I can't really predict the future response of developers using this
feature.  Your "(_,_)" example is something that I, personally, would never
expect a compiler to figure out due to the ambiguity of using the same
symbol in the same context.

On Mon, Nov 21, 2011 at 9:39 AM, Brian Goetz <brian.goetz at oracle.com> wrote:

> We are not planning to add any wunderbar-like feature.  However, Remi has
> pointed out an annoying hole, in that _ is currently a valid identifier
> under JLS 7, and therefore for single-argument lambdas, you *could* say
>
>  _ -> _ + 1
>
> and the compiler would accept it -- but not for the reason you think.
>
> The likely follow-on outcome is that people will *think* we've adopted
> wunderbars, and then wonder why the "stupid" compiler won't accept things
> like
>
>  (_, _) -> _ + _
>
> and probably bitch about "why did you special-case the single-argument
> wunderbar but not the general case".
>
>
>
> On 11/21/2011 10:06 AM, Matthew Adams wrote:
>
>> Hi Remi,
>>
>> I don't understand what you're trying to say.  Are you saying that instead
>> of "it", "#" or empty string (implicit closure param), "_" could be used
>> as
>> an implicit closure param?  If so, then Brian seems to have shot that down
>> in his last email (no Scala wunderbars).  If not, please explain further.
>>
>> -matthew
>>
>> On Sat, Nov 19, 2011 at 3:26 PM, Rémi Forax<forax at univ-mlv.fr>  wrote:
>>
>>  On 11/19/2011 09:45 PM, Brian Goetz wrote:
>>>
>>>> We're pretty satisfied with the degree of syntax reduction we've
>>>>
>>> achieved so far.  You can make things arbitrarily compact, but that's not
>>> the goal.  I don't think that horizontal span is our biggest problem any
>>> more.  So don't expect any Scala-style wunderbars or Groovy-style it.
>>>
>>> and don't forget that even if
>>>
>>>   root.listFiles(it.**lastModified()<= before);
>>>
>>>
>>> is not legal, this snippet is legal because '_' is a legal identifier
>>>
>>>   root.listFiles(_ ->   _.lastModified()<= before);
>>>
>>>
>>> Rémi
>>>
>>>
>>>>
>>>>
>>>>
>>>> On Nov 19, 2011, at 3:10 PM, John Nilsson wrote:
>>>>
>>>>  Given that the usecase for this is about implicit context i really like
>>>>>
>>>> the
>>>
>>>> last option of just leaving the space before the period unfilled.
>>>>>
>>>>> Similarly it would be nice if it worked for all operators:
>>>>>
>>>> list.filter(>2)
>>>
>>>>
>>>>> BR,
>>>>> John million
>>>>> Den 19 nov 2011 00:51 skrev "Matthew Adams"<matthew at matthewadams.me**
>>>>> >:
>>>>>
>>>>>  NB:  I'm searching through the archives on this and didn't see
>>>>>> anything
>>>>>> that directly addressed it.
>>>>>>
>>>>>> I just got through the slides at
>>>>>> http://blogs.oracle.com/**briangoetz/entry/slides_from_**
>>>>>> devoxx_talk_on<http://blogs.oracle.com/briangoetz/entry/slides_from_devoxx_talk_on>
>>>>>> and noticed a nice feature inspired by Groovy that was missing from
>>>>>> the
>>>>>> slide code examples.  I don't know if it's missing from the lambda
>>>>>> proposal, though -- I can't tell from the slides.
>>>>>>
>>>>>> Groovy defaults the name of a single closure argument to "it".  I
>>>>>> think
>>>>>> this would be nice to have in JDK8 lambdas, too.
>>>>>>
>>>>>> =====
>>>>>> // Without "it":
>>>>>> void expire(File root, long before) {
>>>>>> ...
>>>>>> root.listFiles(File p ->   p.lastModified()<= before);
>>>>>> ...
>>>>>> }
>>>>>> =====
>>>>>> // With "it":
>>>>>> void expire(File root, long before) {
>>>>>> ...
>>>>>> root.listFiles(it.**lastModified()<= before);
>>>>>> ...
>>>>>> }
>>>>>> ======
>>>>>>
>>>>>> Is this possible to include, or will the grammar require "->" so that
>>>>>> "it.lastModified<= before" isn't interpreted by the compiler as a
>>>>>>
>>>>> boolean
>>>
>>>> expression?  If that's the case, how about considering "#" (or some
>>>>>>
>>>>> other
>>>
>>>> appropriate character) instead of "it"?  That way, the compiler would
>>>>>>
>>>>> know
>>>
>>>> implicitly that if it encounters a "#", it *must* be a lambda
>>>>>>
>>>>> expression
>>>
>>>> taking a single variable of an inferred type:
>>>>>>
>>>>>> =====
>>>>>> // With "#":
>>>>>> void expire(File root, long before) {
>>>>>> ...
>>>>>> root.listFiles(#.lastModified(**)<= before);
>>>>>> ...
>>>>>> }
>>>>>> ======
>>>>>>
>>>>>> You could even reduce "it" or "#" to an empty string and just use the
>>>>>>
>>>>> "."
>>>
>>>> with no preceding scope.  I don't know if the grammar could support
>>>>>>
>>>>> it, but
>>>
>>>> it's interesting.  I'm not sure I like it, but is sure is compact!
>>>>>>
>>>>>> =====
>>>>>> // With "":
>>>>>> void expire(File root, long before) {
>>>>>> ...
>>>>>> root.listFiles(.lastModified()**<= before);
>>>>>> ...
>>>>>> }
>>>>>> ======
>>>>>>
>>>>>> Another example:
>>>>>> =====
>>>>>> // explicit lambda param name
>>>>>> Set<Album>   favs = albums
>>>>>>    .filter(a ->   a.tracks.anyMatch(t ->   (t.rating>= 4)))
>>>>>>    .into(new HashSet<>());
>>>>>> =====
>>>>>> // "it"
>>>>>> Set<Album>   favs = albums
>>>>>>    .filter(it.tracks.anyMatch(it.**rating>= 4)) // 2 its!?!?
>>>>>>    .into(new HashSet<>());
>>>>>> =====
>>>>>> // "#"
>>>>>> Set<Album>   favs = albums
>>>>>>    .filter(#.tracks.anyMatch(#.**rating>= 4))
>>>>>>    .into(new HashSet<>());
>>>>>> =====
>>>>>> // ""
>>>>>> Set<Album>   favs = albums
>>>>>>    .filter(.tracks.anyMatch(.**rating>= 4))
>>>>>>    .into(new HashSet<>());
>>>>>> =====
>>>>>>
>>>>>> Thoughts?
>>>>>>
>>>>>> -matthew
>>>>>>
>>>>>> --
>>>>>> @matthewadams12
>>>>>> mailto:matthew at matthewadams.me
>>>>>> skype:matthewadams12
>>>>>> yahoo:matthewadams
>>>>>> aol:matthewadams12
>>>>>> google-talk:matthewadams12@**gmail.com<google-talk%3Amatthewadams12 at gmail.com>
>>>>>> msn:matthew at matthewadams.me
>>>>>> http://matthewadams.me
>>>>>> http://www.linkedin.com/in/**matthewadams<http://www.linkedin.com/in/matthewadams>
>>>>>>
>>>>>>
>>>>>>
>>>>
>>>
>>>
>>>
>>
>>


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