No-reuse-streams (original) (raw)

Remi Forax forax at univ-mlv.fr
Mon Nov 26 09:39:38 PST 2012

On 11/26/2012 06:22 PM, Paul Sandoz wrote:

On Nov 26, 2012, at 5:45 PM, Henry Jen <henry.jen at oracle.com> wrote:

On Nov 26, 2012, at 8:21 AM, "David M. Lloyd" <david.lloyd at redhat.com> wrote:

Should the following throw an ISE on the last line of the following?

Stream s = .. Object i1 = s.findFirst(); Stream s1 = s.map(...); i.e. should we fail on the s.map(...) or just when a terminal operation occurs, if at all? I agree with you and Rémi - this should fail.

While it may be "consistent", what is the obvious alternative when need to do something like this? A use case like this is probably following, For a input stream, find a marker, and then continue to process the rest of stream. That seems like a use-case for dropWhile or skipWhile.

take the stream, create an iterator, iterate until you have your marker, wrap the iterator as a new stream (this trick is from Brian). You lost some information about the size of the stream etc, but usually you don't care because on a IO stream these informations are not known.

I guess the general question is: how does one control the flow of the stream? How do we continue the stream after a terminal op which does not consume whole stream. It's a bit funky but one could do: Stream s = ... Iterator i = s.iterator(); Object first = i.next(); i.stream()....; // Not yet supported but IIRC we have talked about making Iterator streamable. If the source is an iterator of some sorts i think detached streams might be useful for repeated processing of such a source. Note that for a parallel stream findFirst and findAny (or anyMatch) may consume more elements than the equivalent sequential stream. Paul.

see above.

Rémi

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