Re: Filter on future doesn't make sense
Avi Levi <[email protected]> Fri, 1 Jul 2016 17:16:56 +0300
| Newsgroups | gmane.comp.lang.scala |
|---|---|
| Message-ID | <CAP0Sp2kOhuJLJ1dt9ryP+K2_S_h-pfeaA_2wwdV5=8+8QeOmLQ@mail.gmail.com> |
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Hi Ronald ,
taking the example above
scala>val x =3D Future{1}.filter(_ =3D=3D 0)
scala>x.value
res2: Option[scala.util.Try[Int]] =3D
Some(Failure(java.util.NoSuchElementException: Future.filter predicate is
not satisfied))
It seems odd that a legit action such as filter yields a failure with an
exception .
Cheers
Avi
2016-07-01 17:02 GMT+03:00 Roland Kuhn <[email protected]>:
> Well =E2=80=A6 technically (and no, this is NOT a good idea, and hence it=
looks a
> little odd):
>
> scala> import concurrent._
> import concurrent._
>
> scala> import ExecutionContext.Implicits._
> import ExecutionContext.Implicits._
>
> scala> import duration._
> import duration._
>
> scala> Future(42)
> res0: scala.concurrent.Future[Int] =3D
> scala.concurrent.impl.Promise$DefaultPromise@25bbf683
>
> scala> Await.ready(res0, 1.second).value.get.toOption
> res1: Option[Int] =3D Some(42)
>
> scala> Await.ready(res0.filter(_ =3D=3D 1), 1.second).value.get.toOption
> res2: Option[Int] =3D None
>
> Regards,
>
> Roland
>
> 1 juli 2016 kl. 15:18 skrev Oliver Ruebenacker <[email protected]>:
>
>
> Hello Roland,
>
> Option has get, getOrElse and the possibility to match against
> Some(value), but Future does not have these.
>
> Best, Oliver
>
> On Fri, Jul 1, 2016 at 9:06 AM, Roland Kuhn <[email protected]> wrote:
>
>> The difference is that Option does not have onComplete: if you restrict
>> yourself to the Option API then Future behaves observably in the same wa=
y.
>> If you want to have something like onComplete you should look at Either[=
NoSuchElementException,
>> T]#fold.
>>
>> In general there is no .filter on monads because that would require the
>> explicit ability to represent emptiness (which is not part of the
>> contract); the success path for the combinators could be seen as such a
>> representation and it is indeed often used as such, so Future is quite
>> well-behaved in this regard. Another comment I=E2=80=99d like to make on=
the
>> discussed change is that it is not reasonable to expect that the result =
of
>> filtering returns a different type than the original one=E2=80=94no othe=
r container
>> has this behavior.
>>
>> Regards,
>>
>> Roland
>>
>>
>> 1 juli 2016 kl. 14:54 skrev Oliver Ruebenacker <[email protected]>:
>>
>>
>> Hello,
>>
>> Looks like sometimes you do get an exception:
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> *Welcome to Scala 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Java
>> 1.8.0_45).Type in expressions for evaluation. Or try :help.scala> import
>> scala.concurrent.Futureimport scala.concurrent.Futurescala> import
>> scala.concurrent.ExecutionContext.Implicits.globalimport
>> scala.concurrent.ExecutionContext.Implicits.globalscala>
>> Future{1}.onComplete { case _ =3D> println("Complete!") }scala>
>> Complete!scala> Future{1}.filter(_ =3D=3D 0).onComplete { case _ =3D>
>> println("Complete!") }Complete!scala> import scala.util.{Success, Failur=
e
>> }import scala.util.{Success, Failure}scala> Future{1}.filter(_ =3D=3D
>> 0).onComplete { | case Success(value) =3D> println(value) | case
>> Failure(ex) =3D> println(ex) | }java.util.NoSuchElementException:
>> Future.filter predicate is not satisfiedscala>*
>>
>> Best, Oliver
>>
>>
>> On Fri, Jul 1, 2016 at 5:44 AM, Viktor Klang <[email protected]>
>> wrote:
>>
>>> I think you are conflating the notion of optionality here.
>>>
>>> option.filter(p).map(f).foreach(println)
>>>
>>> behaves exactly like
>>>
>>> future.filter(p).map(f).foreach(println)
>>>
>>> --
>>> Cheers,
>>> =E2=88=9A
>>> On Jul 1, 2016 11:36 AM, "Avi Levi" <[email protected]> wrote:
>>>
>>>> Correct, just on future you get an exception if element does not pass
>>>> the filter. Wouldn't it be better if we can get something that express=
an
>>>> empty future?
>>>> On Jul 1, 2016 12:30 PM, "Viktor Klang" <[email protected]> wrote=
:
>>>>
>>>>> But you don't get an exception on the success path. All operations on
>>>>> the success path will be skipped, just as for Option.
>>>>>
>>>>> --
>>>>> Cheers,
>>>>> =E2=88=9A
>>>>> On Jul 1, 2016 10:35 AM, "Avi Levi" <[email protected]> wrote:
>>>>>
>>>>>> Hi Victor ,
>>>>>> I totally agree that expectations are subjective .
>>>>>> But like you said a filter on List will return a List if no element
>>>>>> comply than we will get Nil which represents an empty container (emp=
ty list)
>>>>>> a filter on option will return a option if the element doesn't compl=
y
>>>>>> than we will get None which represents an empty container
>>>>>> following the same logic a filter on future should return something
>>>>>> that express empty container , defiantly not an exception, because i=
t is
>>>>>> not an exception we do intend to filter those elements.
>>>>>>
>>>>>>
>>>>>>
>>>>>> 2016-07-01 10:50 GMT+03:00 Viktor Klang <[email protected]>:
>>>>>>
>>>>>>> Hi Avi,
>>>>>>>
>>>>>>> I see what you mean.
>>>>>>>
>>>>>>> I'd want to avoid discussing expectation since it is subjective. I
>>>>>>> will however note that the actualnsemantics of the filter method on=
Future
>>>>>>> needs improvement:
>>>>>>> http://www.scala-lang.org/api/2.11.8/index.html#scala.concurrent.Fu=
ture@filter(p:T=3D
>>>>>>> >Boolean)(implicitexecutor:scala.concurrent.ExecutionContext):scala=
.concurrent.Future[T]
>>>>>>>
>>>>>>> As for might not return the value, the same goes for all
>>>>>>> filter-methods:
>>>>>>>
>>>>>>> List returns List, but it might not have any elements at all. Optio=
n
>>>>>>> returns Option but can be Some or None, Future is either Success or=
Failure.
>>>>>>>
>>>>>>> If success has an optionality aspect in your usage, use Future of
>>>>>>> Option to express that, that would be my recommendation.
>>>>>>>
>>>>>>> --
>>>>>>> Cheers,
>>>>>>> =E2=88=9A
>>>>>>> On Jul 1, 2016 9:20 AM, "Avi Levi" <[email protected]> wrote:
>>>>>>>
>>>>>>>> Thanks Victor,
>>>>>>>> Of course it can be implemented as you suggested. But still I can
>>>>>>>> argue that the current implementation is not "really filtering" th=
e results
>>>>>>>> as one might expect and less expressive if it might or not return =
the value
>>>>>>>> than Option is more expressive, don't you agree?
>>>>>>>> On Jul 1, 2016 10:06 AM, "Viktor Klang" <[email protected]>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> Hi Avi,
>>>>>>>>>
>>>>>>>>> Use Fututre[Option[Int]] if you want to deal with Some/None as a
>>>>>>>>> result of filter ( f.map(_.filter(p) ) (alt. see monad transforme=
rs)
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> Cheers,
>>>>>>>>> =E2=88=9A
>>>>>>>>> On Jul 1, 2016 8:53 AM, "Avi Levi" <[email protected]> wrote:
>>>>>>>>>
>>>>>>>>> I was trying to figure out what should I accept when filtering
>>>>>>>>> over a future .
>>>>>>>>> the current implementation yields either a T or an exception whic=
h
>>>>>>>>> kind of breaks referential transparency (doesn't it ?) .
>>>>>>>>> on the other hand what can I expect given this expression
>>>>>>>>>
>>>>>>>>> *def foo(i:Int):Future[Int]*
>>>>>>>>>
>>>>>>>>> the type result of
>>>>>>>>>
>>>>>>>>> *foo(1).filter(_ % 2 =3D=3D 0)*
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I.M.H.O I would expect it to yield Option[T] which makes more
>>>>>>>>> sense to express that we might get a value that pass the filter o=
r not . is
>>>>>>>>> that make sense ?
>>>>>>>>>
>>>>>>>>> Cheers
>>>>>>>>> Avi
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> You received this message because you are subscribed to the Googl=
e
>>>>>>>>> Groups "scala-language" group.
>>>>>>>>> To unsubscribe from this group and stop receiving emails from it,
>>>>>>>>> send an email to [email protected].
>>>>>>>>> For more options, visit https://groups.google.com/d/optout.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> --
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n
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>>>>>>>>> .
>>>>>>>>> To unsubscribe from this group and all its topics, send an email
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>>>>>>>>>
>>>>>>>>
>>>>>>>> --
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>>>>>>>
>>>>>>> --
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>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Sincerely,
>>>>>> Avi Levi
>>>>>> m: +972-52-3459959
>>>>>> <https://www.linkedin.com/in/leviavi>
>>>>>> https://about.me/avi.levi
>>>>>>
>>>>>> --
>>>>>> You received this message because you are subscribed to the Google
>>>>>> Groups "scala-language" group.
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>>>>>>
>>>>>
>>>>> --
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e
>>>>> Google Groups "scala-language" group.
>>>>> To unsubscribe from this topic, visit
>>>>> https://groups.google.com/d/topic/scala-language/wpGOB8f7qmY/unsubscr=
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>>>>> .
>>>>> To unsubscribe from this group and all its topics, send an email to
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>>>>>
>>>>
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>>>
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>>>
>>
>>
>>
>> --
>> Oliver Ruebenacker
>> Senior Software Engineer, Diabetes Portal
>> <http://www.type2diabetesgenetics.org/>, Broad Institute
>> <http://www.broadinstitute.org/>
>>
>>
>> --
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s
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>>
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n
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>>
>
>
>
> --
> Oliver Ruebenacker
> Senior Software Engineer, Diabetes Portal
> <http://www.type2diabetesgenetics.org/>, Broad Institute
> <http://www.broadinstitute.org/>
>
>
> --
> You received this message because you are subscribed to the Google Groups
> "scala-language" group.
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>
>
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--=20
Sincerely,
Avi Levi
m: +972-52-3459959
<https://www.linkedin.com/in/leviavi>
https://about.me/avi.levi
--=20
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<div dir=3D"rtl"><div dir=3D"ltr">Hi Ronald ,</div><div dir=3D"ltr">taking =
the example above=C2=A0</div><div dir=3D"ltr">scala>val x =3D Future{1}.=
filter(_ =3D=3D 0)</div><div dir=3D"ltr"><div dir=3D"ltr">scala>x.value<=
/div><div dir=3D"ltr">res2: Option[scala.util.Try[Int]] =3D Some(Failure(ja=
va.util.NoSuchElementException: Future.filter predicate is not satisfied))<=
/div></div><div dir=3D"ltr"><br></div><div dir=3D"ltr">It seems odd that a =
legit action such as filter yields a failure with an exception .=C2=A0<br><=
/div><div dir=3D"ltr"><br></div><div dir=3D"ltr">Cheers=C2=A0</div><div dir=
=3D"ltr">Avi</div><div dir=3D"ltr"><div><br></div></div></div><div class=3D=
"gmail_extra"><br><div class=3D"gmail_quote"><div dir=3D"ltr">2016-07-01 17=
:02 GMT+03:00 Roland Kuhn <span dir=3D"ltr"><<a href=3D"mailto:google@rk=
uhn.info" target=3D"_blank">[email protected]</a>></span>:</div><blockqu=
ote class=3D"gmail_quote" style=3D"margin:0 .8ex;border-left:1px #ccc solid=
;border-right:1px #ccc solid;padding-left:1ex;padding-right:1ex"><div style=
=3D"word-wrap:break-word">Well =E2=80=A6 technically (and no, this is NOT a=
good idea, and hence it looks a little odd):<div><br></div><div><div><font=
face=3D"Courier">scala> import concurrent._</font></div><div><font face=
=3D"Courier">import concurrent._</font></div><div><font face=3D"Courier"><b=
r></font></div><div><font face=3D"Courier">scala> import ExecutionContex=
t.Implicits._</font></div><div><font face=3D"Courier">import ExecutionConte=
xt.Implicits._</font></div><div><font face=3D"Courier"><br></font></div><di=
v><font face=3D"Courier">scala> import duration._</font></div><div><font=
face=3D"Courier">import duration._</font></div><div><font face=3D"Courier"=
><br></font></div><div><font face=3D"Courier">scala> Future(42)</font></=
div><div><font face=3D"Courier">res0: scala.concurrent.Future[Int] =3D scal=
a.concurrent.impl.Promise$DefaultPromise@25bbf683</font></div><div><font fa=
ce=3D"Courier"><br></font></div><div><font face=3D"Courier">scala> Await=
.ready(res0, 1.second).value.get.toOption</font></div><div><font face=3D"Co=
urier">res1: Option[Int] =3D Some(42)</font></div></div><div><font face=3D"=
Courier"><br></font></div><div><font face=3D"Courier"><div>scala> Await.=
ready(res0.filter(_ =3D=3D 1), 1.second).value.get.toOption</div><div>res2:=
Option[Int] =3D None</div></font></div><div><br></div><div>Regards,</div><=
div><br></div><div>Roland</div><div><div class=3D"h5"><div><br><div><blockq=
uote type=3D"cite"><div>1 juli 2016 kl. 15:18 skrev Oliver Ruebenacker <=
<a href=3D"mailto:[email protected]" target=3D"_blank">[email protected]</a>&=
gt;:</div><br><div><div dir=3D"ltr"><div><div><div><br></div>=C2=A0=C2=A0=
=C2=A0=C2=A0 Hello Roland,<br><br></div>=C2=A0 Option has get, getOrElse an=
d the possibility to match against Some(value), but Future does not have th=
ese.<br><br></div>=C2=A0=C2=A0=C2=A0=C2=A0 Best, Oliver<br></div><div class=
=3D"gmail_extra"><br><div class=3D"gmail_quote">On Fri, Jul 1, 2016 at 9:06=
AM, Roland Kuhn <span dir=3D"ltr"><<a href=3D"mailto:[email protected]"=
target=3D"_blank">[email protected]</a>></span> wrote:<br><blockquote c=
lass=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;=
padding-left:1ex"><div style=3D"word-wrap:break-word">The difference is tha=
t Option does not have onComplete: if you restrict yourself to the Option A=
PI then Future behaves observably in the same way. If you want to have some=
thing like onComplete you should look at <font face=3D"Courier">Either[NoSu=
chElementException, T]#fold</font>.<div><br></div><div>In general there is =
no .filter on monads because that would require the explicit ability to rep=
resent emptiness (which is not part of the contract); the success path for =
the combinators could be seen as such a representation and it is indeed oft=
en used as such, so Future is quite well-behaved in this regard. Another co=
mment I=E2=80=99d like to make on the discussed change is that it is not re=
asonable to expect that the result of filtering returns a different type th=
an the original one=E2=80=94no other container has this behavior.</div><div=
><br></div><div>Regards,</div><div><br></div><div>Roland<div><div><br><div>=
<br><div><blockquote type=3D"cite"><div>1 juli 2016 kl. 14:54 skrev Oliver =
Ruebenacker <<a href=3D"mailto:[email protected]" target=3D"_blank">curol=
[email protected]</a>>:</div><br><div><div dir=3D"ltr"><div><div><br></div>=C2=
=A0=C2=A0=C2=A0=C2=A0 Hello,<br><br></div>=C2=A0 Looks like sometimes you d=
o get an exception:<br><div><div><br><b><span style=3D"font-family:monospac=
e,monospace">Welcome to Scala 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Ja=
va 1.8.0_45).<br>Type in expressions for evaluation. Or try :help.<br><br>s=
cala> import scala.concurrent.Future<br>import scala.concurrent.Future<b=
r><br>scala> import scala.concurrent.ExecutionContext.Implicits.global<b=
r>import scala.concurrent.ExecutionContext.Implicits.global<br><br>scala>=
; Future{1}.onComplete { case _ =3D> println("Complete!") }<br=
><br>scala> Complete!<br><br><br>scala> Future{1}.filter(_ =3D=3D 0).=
onComplete { case _ =3D> println("Complete!") }<br>Complete!<b=
r><br>scala> import scala.util.{Success, Failure }<br>import scala.util.=
{Success, Failure}<br><br>scala> Future{1}.filter(_ =3D=3D 0).onComplete=
{<br>=C2=A0=C2=A0=C2=A0=C2=A0 | case Success(value) =3D> println(value)=
<br>=C2=A0=C2=A0=C2=A0=C2=A0 | case Failure(ex) =3D> println(ex)<br>=C2=
=A0=C2=A0=C2=A0=C2=A0 | }<br><br>java.util.NoSuchElementException: Future.f=
ilter predicate is not satisfied<br>scala></span></b><br><br></div><div>=
=C2=A0=C2=A0=C2=A0=C2=A0 Best, Oliver<br></div><div><br></div></div></div><=
div class=3D"gmail_extra"><br><div class=3D"gmail_quote">On Fri, Jul 1, 201=
6 at 5:44 AM, Viktor Klang <span dir=3D"ltr"><<a href=3D"mailto:viktor.k=
[email protected]" target=3D"_blank">[email protected]</a>></span> wro=
te:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-=
left:1px #ccc solid;padding-left:1ex"><p dir=3D"ltr">I think you are confla=
ting the notion of optionality here.</p><p dir=3D"ltr">option.filter(p).map=
(f).foreach(println)</p><p dir=3D"ltr">behaves exactly like</p><p dir=3D"lt=
r">future.filter(p).map(f).foreach(println)</p><span><font color=3D"#888888=
"><p dir=3D"ltr">-- <br>
Cheers,<br>
=E2=88=9A</p></font></span><div><div>
<div class=3D"gmail_quote">On Jul 1, 2016 11:36 AM, "Avi Levi" &l=
t;<a href=3D"mailto:[email protected]" target=3D"_blank">[email protected]</a=
>> wrote:<br type=3D"attribution"><blockquote class=3D"gmail_quote" styl=
e=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><p dir=
=3D"ltr">Correct, just on future you get an exception if element does not p=
ass the filter. Wouldn't it be better if we can get something that expr=
ess an empty future? </p>
<div class=3D"gmail_quote">On Jul 1, 2016 12:30 PM, "Viktor Klang"=
; <<a href=3D"mailto:[email protected]" target=3D"_blank">viktor.kl=
[email protected]</a>> wrote:<br type=3D"attribution"><blockquote class=3D"g=
mail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-l=
eft:1ex"><p dir=3D"ltr">But you don't get an exception on the success p=
ath. All operations on the success path will be skipped, just as for Option=
.</p><p dir=3D"ltr">-- <br>
Cheers,<br>
=E2=88=9A</p>
<div class=3D"gmail_quote">On Jul 1, 2016 10:35 AM, "Avi Levi" &l=
t;<a href=3D"mailto:[email protected]" target=3D"_blank">[email protected]</a=
>> wrote:<br type=3D"attribution"><blockquote class=3D"gmail_quote" styl=
e=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div di=
r=3D"rtl"><div dir=3D"ltr">Hi Victor ,</div><div dir=3D"ltr">I totally agre=
e that expectations are subjective .</div><div dir=3D"ltr">But like you sai=
d a filter on List will return a List if no element comply than we will get=
Nil which represents an empty container (empty list)</div><div dir=3D"ltr"=
>a filter on option will return a option if the element doesn't comply =
than we will get None which represents an empty container=C2=A0</div><div d=
ir=3D"ltr">following the same logic a filter on future should return someth=
ing that express empty container , defiantly not an exception, because it i=
s not an exception we do intend to filter those elements.</div><div dir=3D"=
ltr"><br></div><div dir=3D"ltr">=C2=A0</div></div><div class=3D"gmail_extra=
"><br><div class=3D"gmail_quote"><div dir=3D"ltr">2016-07-01 10:50 GMT+03:0=
0 Viktor Klang <span dir=3D"ltr"><<a href=3D"mailto:[email protected]=
om" target=3D"_blank">[email protected]</a>></span>:</div><blockquo=
te class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc so=
lid;padding-left:1ex"><p dir=3D"ltr">Hi Avi,</p><p dir=3D"ltr">I see what y=
ou mean.</p><p dir=3D"ltr">I'd want to avoid discussing expectation sin=
ce it is subjective. I will however note that the actualnsemantics of the f=
ilter method on Future needs improvement: <a href=3D"http://www.scala-lang.=
org/api/2.11.8/index.html#scala.concurrent.Future@filter(p:T=3D" target=3D"=
_blank">http://www.scala-lang.org/api/2.11.8/index.html#scala.concurrent.Fu=
ture@filter(p:T=3D</a>>Boolean)(implicitexecutor:scala.concurrent.Execut=
ionContext):scala.concurrent.Future[T]</p><p dir=3D"ltr">As for might not r=
eturn the value, the same goes for all filter-methods:</p><p dir=3D"ltr">Li=
st returns List, but it might not have any elements at all. Option returns =
Option but can be Some or None, Future is either Success or Failure.</p><p =
dir=3D"ltr">If success has an optionality aspect in your usage, use Future =
of Option to express that, that would be my recommendation. </p><span><font=
color=3D"#888888"><p dir=3D"ltr">-- <br>
Cheers,<br>
=E2=88=9A</p></font></span><div><div>
<div class=3D"gmail_quote">On Jul 1, 2016 9:20 AM, "Avi Levi" <=
;<a href=3D"mailto:[email protected]" target=3D"_blank">[email protected]</a>=
> wrote:<br type=3D"attribution"><blockquote class=3D"gmail_quote" style=
=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><p dir=
=3D"ltr">Thanks Victor,<br>
Of course it can be implemented as you suggested. But still I can argue th=
at the current implementation is not "really filtering" the resul=
ts as one might expect and less expressive if it might or not return the va=
lue than Option is more expressive, don't you agree? </p>
<div class=3D"gmail_quote">On Jul 1, 2016 10:06 AM, "Viktor Klang"=
; <<a href=3D"mailto:[email protected]" target=3D"_blank">viktor.kl=
[email protected]</a>> wrote:<br type=3D"attribution"><blockquote class=3D"g=
mail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-l=
eft:1ex"><p dir=3D"ltr">Hi Avi,</p><p dir=3D"ltr">Use Fututre[Option[Int]] =
if you want to deal with Some/None as a result of filter ( f.map(_.filter(p=
) ) (alt. see monad transformers)</p><p dir=3D"ltr">-- <br>
Cheers,<br>
=E2=88=9A</p>
<div class=3D"gmail_quote">On Jul 1, 2016 8:53 AM, "Avi Levi" <=
;<a href=3D"mailto:[email protected]" target=3D"_blank">[email protected]</a>=
> wrote:<br type=3D"attribution"><blockquote style=3D"margin:0 0 0 .8ex;=
border-left:1px #ccc solid;padding-left:1ex"><div dir=3D"ltr">I was trying =
to figure out what should I accept when filtering over a future .<div>the c=
urrent implementation yields either a T or an exception which kind of break=
s referential transparency (doesn't it ?) .</div><div>on the other hand=
what can I expect given this expression=C2=A0</div><div><p><span><i>def fo=
o(i:Int):Future[Int]</i></span></p><p><span>the type result of=C2=A0</span>=
</p><p><i>foo(1).filter(_ % 2 =3D=3D 0)</i></p><p><span><br></span></p></di=
v><div>I.M.H.O I would expect it to yield Option[T] =C2=A0which makes more =
sense to express that we might get a value that pass the filter or not . is=
that make sense ?</div><div><br></div><div>Cheers</div><font color=3D"#888=
888"><div>Avi=C2=A0</div></font></div><font color=3D"#888888"><div><br></di=
v>
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tl"><div><div dir=3D"rtl"><div dir=3D"ltr"><span style=3D"color:rgb(51,51,5=
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</div></div></blockquote></div><br><br clear=3D"all"><br>-- <br><div data-s=
martmail=3D"gmail_signature"><div dir=3D"ltr"><div><div dir=3D"ltr"><div><d=
iv dir=3D"ltr"><div><div dir=3D"ltr"><div>Oliver Ruebenacker<br></div><div>=
Senior Software Engineer, <a href=3D"http://www.type2diabetesgenetics.org/"=
target=3D"_blank">Diabetes Portal</a>, <a href=3D"http://www.broadinstitut=
e.org/" target=3D"_blank">Broad Institute</a><br></div><br></div></div></di=
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martmail=3D"gmail_signature"><div dir=3D"ltr"><div><div dir=3D"ltr"><div><d=
iv dir=3D"ltr"><div><div dir=3D"ltr"><div>Oliver Ruebenacker<br></div><div>=
Senior Software Engineer, <a href=3D"http://www.type2diabetesgenetics.org/"=
target=3D"_blank">Diabetes Portal</a>, <a href=3D"http://www.broadinstitut=
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<div class=3D"h5">
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