RFR : JDK-8001642 : Add Optional<T>, OptionalDouble, OptionalInt, OptionalLong

Remi Forax forax at univ-mlv.fr
Wed Mar 6 03:58:43 PST 2013

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.

> 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.


> On 06/03/2013, at 8:47 PM, Remi Forax <forax at 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

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