Stream.limit() - puzzler/bug/feature

[Zhong Yu]

People don't have this problem with InputStream, so it's probably not
a big deal.

On Thu, Nov 15, 2012 at 12:10 PM, Sam Pullara <spullara at gmail.com> wrote:
> This was my thinking when I read the example. Not sure if that is practical but it might reduce errors such as the one described.
>
> Sam
>
> On Nov 15, 2012, at 9:36 AM, Remi Forax <forax at univ-mlv.fr> wrote:
>
>> On 11/15/2012 06:22 PM, Brian Goetz wrote:
>>> The best way to think about it is that a Stream is more like an Iterator
>>> than a data structure.  There is some abstract source of data somewhere
>>> (it might be in a data structure, or might be generated from a function,
>>> or read from a network), and a series of transformations applied to the
>>> data between the source and the consumer.  Streams can additionally
>>> execute using parallelism, if requested.
>>>
>>> Stream constructs like:
>>>
>>> Stream<Person> s = people.stream()
>>>                           .filter(p -> p.getLastName().equals("Smith")))
>>>
>>> do not do any filtering on construction.  It simply says "there's a
>>> stream source, the collection 'people', and when you consume from the
>>> stream s, you'll get the results of filtering the source values."
>>>
>>> The confusion in Dmitry's example is akin to multiple activities reading
>>> from the same IO channel -- they might interfere with each other over
>>> who gets the next value, and any buffering that any consumer does may
>>> confuse other consumers.
>>
>> Maybe the implementation should protect users to use two aliases of a
>> non-replayable stream.
>> Using the example of Dmitry, if the stream is an IO channel, the second
>> call to limit() or to any method of 's' should throw an
>> IllegalStateException.
>>
>> Rémi
>>
>>>
>>>
>>>
>>> On 11/15/2012 12:11 PM, Marcus Thiesen wrote:
>>>> Hey List,
>>>>
>>>> sorry, I haven't followed the whole Stream discussion and without publicliy
>>>> available JavaDocs (are there?) I'm currently trying to figure out what
>>>> this comment means, because without all that background I read the code as
>>>> annotated:
>>>>
>>>> 2012/11/15 Dmitry Bessonov <dmitry.bessonov at oracle.com>
>>>>
>>>>> While playing with method Sream.limit(int) using a mini-code like
>>>>>
>>>>>           final Stream<Integer> s = Arrays.asStream(1, 2, 3, 4, 5);
>>>>>
>>>> Give me a "Stream" view of the Array int[] 1, 2, 3, 4, 5.
>>>>
>>>>
>>>>
>>>>>           final Stream<Integer> to3 = s.limit(3);
>>>>>
>>>> Give me a Stream view of s limitted to 3 values.
>>>>
>>>>
>>>>>           final Stream<Integer> to4 = s.limit(4);
>>>>>
>>>> Give me a Stream view of s limitted to 4 values.
>>>>
>>>>
>>>>> have to admit that there's no unambiguous answer
>>>>> to the question of contents  of streams "to3" and "to4".
>>>>> It depends on which of the streams is consumed first.
>>>>>
>>>>>
>>>> My best guess would be to3 = [ 1, 2, 3 ] and to4 = [ 1, 2, 3, 4 ].
>>>>
>>>> Given my naive understanding of the above code the comment does not make
>>>> sense. The only way the above comment makes sense is that we are not
>>>> talking of (somehow immutable) views here but that those operations mutate
>>>>   the backing array on read time of the resulting stream. Am I right?
>>>>
>>>> Cheers,
>>>>    Marcus
>>>>
>>>>
>>>>
>>>>
>>
>>
>
>