On Tue, 3 Nov 2020 01:33:32 GMT, Stuart Marks <sma...@openjdk.org> wrote:
> This change introduces a new terminal operation on Stream. This looks like a > convenience method for Stream.collect(Collectors.toList()) or > Stream.collect(Collectors.toUnmodifiableList()), but it's not. Having this > method directly on Stream enables it to do what can't easily by done by a > Collector. In particular, it allows the stream to deposit results directly > into a destination array (even in parallel) and have this array be wrapped in > an unmodifiable List without copying. > > In the past we've kept most things from the Collections Framework as > implementations of Collector, not directly on Stream, whereas only > fundamental things (like toArray) appear directly on Stream. This is true of > most Collections, but it does seem that List is special. It can be a thin > wrapper around an array; it can handle generics better than arrays; and > unlike an array, it can be made unmodifiable (shallowly immutable); and it > can be value-based. See John Rose's comments in the bug report: > > https://bugs.openjdk.java.net/browse/JDK-8180352?focusedCommentId=14133065&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14133065 > > This operation is null-tolerant, which matches the rest of Streams. This > isn't specified, though; a general statement about null handling in Streams > is probably warranted at some point. > > Finally, this method is indeed quite convenient (if the caller can deal with > what this operation returns), as collecting into a List is the most common > stream terminal operation. src/java.base/share/classes/java/util/stream/Stream.java line 1192: > 1190: @SuppressWarnings("unchecked") > 1191: default List<T> toList() { > 1192: return (List<T>) Collections.unmodifiableList(new > ArrayList<>(Arrays.asList(this.toArray()))); Why can't we return `listFromTrustedArrayNullsAllowed` here as in `ReferencePipeline`? Or at least, we should avoid unnecessary copying of arrays. See [how this is done](https://github.com/amaembo/streamex/blob/master/src/main/java/one/util/streamex/AbstractStreamEx.java#L1313) in StreamEx. ------------- PR: https://git.openjdk.java.net/jdk/pull/1026
