Whatever happened to the elvis operator solution from project coin, surely that solves the majority of issues Optional was meant to solve anyway, without the headache of type-mix mud clutering up the code.
http://mail.openjdk.java.net/pipermail/coin-dev/2009-March/000047.html _____ From: Remi Forax [mailto:fo...@univ-mlv.fr] To: Jed Wesley-Smith [mailto:jed.wesleysm...@gmail.com] Cc: lambda-libs-spec-expe...@openjdk.java.net [mailto:lambda-libs-spec-expe...@openjdk.java.net], lambda-...@openjdk.java.net [mailto:lambda-...@openjdk.java.net], core-libs-dev@openjdk.java.net [mailto:core-libs-dev@openjdk.java.net] Sent: Wed, 06 Mar 2013 11:58:43 +0000 Subject: Re: RFR : JDK-8001642 : Add Optional<T>, OptionalDouble, OptionalInt, OptionalLong On 03/06/2013 11:54 AM, Jed Wesley-Smith wrote: > Really, this is a lot of fuss over nothing. > > There is actually no fundamental difference between Scala's Option, Guava's Optional, Fugue's Option, Java's Optional and Haskell's Maybe – they are modelling the same thing, the possibility of a value not being present. > > The fact that there may be minor differences in api or semantics around whether null is a legal value are minor in the scheme of things (and yes, null is a pretty stupid legal value of a Some IMHO). > > Stephen's example is ludicrous, why have a list of optional values? You'd flatten down into just a list – and an optional list only makes sense if the enclosed list is guaranteed to be non-empty, otherwise you just return an empty list! People like shooting their own feet. http://cs.calstatela.edu/wiki/index.php/Courses/CS_460/Fall_2012/Week_8/gamePlay.combat.BattleAnalysis > > If we are going to use potential straw-men as arguments we can stall all progress. Please concentrate on the important matters, let's disavow null as a valid value and save us all a billion dollars Also Scala Option is not the only way to solve the null problem. The JSR308 annotation @Nullable/@NonNull are recognized by Eclipse and IntelliJ at least. > . > > cheers, > jed. cheers, Rémi > > On 06/03/2013, at 8:47 PM, Remi Forax <fo...@univ-mlv.fr> wrote: > >> Ok, let be nuclear on this, >> There is no good reason to introduce Optional<T> in java.util. >> >> It doen't work like Google's Guava Optional despite having the same >> name, it doesn't work like Scala's Option despite having a similar name, >> moreover the lambda pipeline face a similar issue with the design of >> collectors (see stream.collect()) but solve that similar problem with a >> different design, so the design of Optional is not even consistent with >> the rest of the stream API. >> >> So why do we want something like Optional, we want it to be able to >> represent the fact that as Mike states a returning result can have no >> value by example Colections.emptyList().stream().findFirst() should >> 'return' no value. >> >> As Stephen Colebourne said, Optional is a bad name because Scala uses >> Option [1] which can used in the same context, as result of a filter/map >> etc. but Option in Scala is a way to mask null. Given the name >> proximity, people will start to use Optional like Option in Scala and we >> will see methods returning things like Optional<List<Optional<String>>>. >> >> Google's Guava, which is a popular library, defines a class named >> Optional, but allow to store null unlike the current proposed >> implementation, this will generate a lot of confusions and frustrations. >> >> In fact, we don't need Optional at all, because we don't need to return >> a value that can represent a value or no value, >> the idea is that methods like findFirst should take a lambda as >> parameter letting the user to decide what value should be returned by >> findFirst if there is a value and if there is no value. >> So instead of >> stream.findFirst().orElse(null) >> you will write >> stream.findFirst(orNull) >> with orNull() defined as like that >> public static <T> Optionalizer orNull() { >> return (isPresent, element) -> isPresent? element: null; >> } >> >> The whole design is explained here [2] and is similar to the way >> Collectors are defined [3], >> it's basically the lambda way of thinking, instead of creating an object >> representing the different states resulting of a call to findFirst, >> findFirst takes a lambda as parameter which is fed with the states of a >> call. >> >> cheers, >> Rémi >> >> [1] http://www.scala-lang.org/api/current/index.html#scala.Option >> [2] >> http://mail.openjdk.java.net/pipermail/lambda-libs-spec-observers/2013-February/001470.html >> [3] >> http://hg.openjdk.java.net/lambda/lambda/jdk/file/tip/src/share/classes/java/util/stream/Collectors.java >> >> >> On 03/04/2013 09:29 PM, Mike Duigou wrote: >>> Hello All; >>> >>> This patch introduces Optional container objects to be used by the lambda streams libraries for returning results. >>> >>> The reference Optional type, as defined, intentionally does not allow null values. null may be used with the Optional.orElse() method. >>> >>> All of the Optional types define hashCode() and equals implementations. Use of Optional types in collections should be generally discouraged but having useful equals() and hashCode() is ever so convenient. >>> >>> http://cr.openjdk.java.net/~mduigou/JDK-8001642/0/webrev/ >>> >>> Mike >>> >>
