Thanks for the review. Editorial comments accepted. Discussion and responses to
some items below.
On 10/31/17 7:25 AM, Brian Goetz wrote:
Returns an <a href="#unmodifiable">unmodifiable Map</a> containing the entries
1664 * of the given Map. the given Map must not be null, and it must not
contain any
1665 * null keys or values. If the given Map is subsequently modified, the
returned
1666 * Map will not reflect such modifications.
I might quibble with "subsequently modified", as there is some ambiguity (what
if the map is concurrently modified, subsequent to making the copyOf() call,
but prior to the return from copyOf()?) But I won't ;)
Well I actually did think about this, but I couldn't think of anything better to
say. If concurrent modification is permitted, it's conceivable that a
modification made any time during the copy might end up in the returned map. It
depends on the source map's implementation and concurrent modification policy.
So I think the only statement that can be made is about the state of the
returned map after copyOf() returns. That's what "subsequent" means to me, but I
could clarify this if you think it's worth it.
(Similar reasoning for List and Set.)
296 Collector<T, ?, List<T>> toUnmodifiableList() {
297 return new CollectorImpl<>((Supplier<List<T>>) ArrayList::new, List::add,
298 (left, right) -> { left.addAll(right); return left; },
299 list -> (List<T>)List.of(list.toArray()),
300 CH_NOID);
why the intermediate array, and not just use copyOf()? (Is it because you
added copyOf later and didn't go back and update this?) Same for other
collectors.
The copyOf method is mostly forced to make a defensive copy, so it's no better.
I think what should happen here eventually is that the elements should be
collected into something like a SpinedBuffer, and then a private interface
should be plumbed into the unmodifiable list implementation that can copy
elements directly from the buffer. This avoids the extra copy. But I'll take
care of that later.
For toUnmodifiableSet and toUnmodifiableMap, I can imagine similar private
interfaces to avoid excess copies, but I think they each still need to build up
full intermediate HashSet/HashMap in order to get rid of duplicates.
s'marks
On 10/30/2017 6:50 PM, Stuart Marks wrote:
(also includes 8184690: add Collectors for collecting into unmodifiable List,
Set, and Map)
Hi all,
Here's an updated webrev for this changeset; the previous review thread is here:
http://mail.openjdk.java.net/pipermail/core-libs-dev/2017-September/049261.html
This webrev includes the following:
* specification revisions to provide clearer definitions of "view"
collections, "unmodifiable" collections, and "unmodifiable views"
* new List.copyOf(), Set.copyOf(), and Map.copyOf() "copy factory" methods
* new Collectors.toUnmodifiableList, Set, and Map methods
* tests for the new API methods
I've added some assertions that require some independence between the source
collection (or map) and the result of the copyOf() method.
I've made a small but significant change to Set.copyOf compared to the
previous round. Previously, it specified that the first of any equal elements
was preserved. Now, it is explicitly unspecified which of any equals elements
is preserved. This is consistent with Set.addAll, Collectors.toSet, and the
newly added Collectors.toUnmodifiableSet, none of which specify which of
duplicate elements is preserved.
(The outlier here is Stream.distinct, which specifies that the first element
of any duplicates is preserved, if the stream is ordered.)
I've also made some minor wording/editorial changes in response to
suggestions from David Holmes and Roger Riggs. I've kept the wording changes
that give emphasis to "unmodifiable" over "immutable." The term "immutable"
is inextricably intertwined with "persistent" when it comes to data
structures, and I believe we'll be explaining this forever if Java's
"immutable" means something different from everybody else's.
Webrev:
http://cr.openjdk.java.net/~smarks/reviews/8177290/webrev.1/
Bugs:
https://bugs.openjdk.java.net/browse/JDK-8177290
add copy factory methods for unmodifiable List, Set, Map
https://bugs.openjdk.java.net/browse/JDK-8184690
add Collectors for collecting into unmodifiable List, Set, and Map
Thanks,
s'marks
