On Jul 14, 2014, at 12:57 PM, Remi Forax <fo...@univ-mlv.fr> wrote:
>
> On 07/14/2014 12:51 PM, Paul Sandoz wrote:
>> On Jul 12, 2014, at 5:41 PM, Remi Forax <fo...@univ-mlv.fr> wrote:
>>
>>> I was not able to find the answer to my question in the archive,
>>> why Stream.concat is not implemented like this ?
>>>
>>> @SafeVarargs
>>> public static <T> Stream<T> concat(Stream<T>... streams) {
>>> return Arrays.stream(streams).flatMap(Function.identity());
>>> }
>>>
>> Because the capabilities and characteristics of the streams are then lost
>> e.g. in this case the splitting is governed by the number of streams passed
>> in.
>
> it seems to be a limitation of flatMap in that case, no ?
>
That would be much harder to optimise since each element gets mapped to a
Stream of 0 or more elements when the pipeline is executed. The operation has
no "global" view of all the streams to concatenate as all it knows is a mapping
function. At the moment flatMap is quite a simple and efficient stateless
operation and i think it best it stays that way.
e.g. imagine the case of streaming over the lines of a file and flatMapping
each line to one or more words.
Paul.
