Re: Different behaviour from Option map in scala compared to Optional map in java

Hello,

There are good reasons that .map() does not change `null` to `None`. If it
did that, I would never be able to use a `.map` on an `Option[T]` where I
myself do not know what T will be (typically, because I'm writing a
library). The user of my library might very well use my library with a T
that can reasonably contain null values. In the insides of my library,
using a null-handling .map() would *destroy* the data of my user. In other
words, such a map would not be completely *type parametric*.

If you want a .map() that takes care of `null` returned by its function,
you can use `.flatMap(x => Option(f(x)))`.

Cheers,
Sébastien

On Sun, Apr 17, 2016 at 6:30 PM, Vlad Patryshev <[email protected]>
wrote:

> I agree; Some(null) is an abomination, and Option(f(this.get)) would make
> more sense.
>
> Actually, in my class Result I wrap all these things (exceptions and
> nulls) even for filter and collect, not just map. Meaning, if the predicate
> called in filter() throws an exception, that's a legit error, and should be
> wrapped as Bad(exception). I think, David Pollak's Box does the same.
>
> Thanks,
> -Vlad
>
> On Sun, Apr 17, 2016 at 3:27 AM, Marc Arndt <[email protected]> wrote:
>
>> Hello,
>> while programming with java 8 and scala I discovered that both seem to
>> have a different behaviour with the method map in the classes Option in
>> scala and Optional in java.
>> In scala the method map in Option is implemented as followed:
>>
>>
>> *  @inline final def map[B](f: A => B): Option[B] =    if (isEmpty) None
>> else Some(f(this.get))*This method requires, that f doesn't return null.
>>
>> In java the method map in Optional is implemented as followed:
>>
>>
>>
>>
>>
>>
>>
>> *    public<U> Optional<U> map(Function<? super T, ? extends U> mapper)
>> {        Objects.requireNonNull(mapper);        if
>> (!isPresent())            return empty();        else {            return
>> Optional.ofNullable(mapper.apply(value));        }    }*
>> This method does not require, that the given method returns a value not
>> null, it is also accepted to return null.
>>
>> I'm not sure if this behaviour is intended.
>>
>> Many Greetings
>> Marc
>>
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