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
