Stream.concat (original) (raw)

Remi Forax forax at univ-mlv.fr
Mon Jul 14 15:00:32 UTC 2014

On 07/14/2014 01:37 PM, Paul Sandoz wrote:

On Jul 14, 2014, at 12:57 PM, Remi Forax <forax at univ-mlv.fr> wrote:

On 07/14/2014 12:51 PM, Paul Sandoz wrote: On Jul 12, 2014, at 5:41 PM, Remi Forax <forax at 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 Stream concat(Stream... 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.

and imagine the case where you know the size of a stream returned by flatMap, in that case, you may want to split before pumping the values of the stream.

Rémi

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