RFR: 8266571: Sequenced Collections

[Viktor Klang]

On Tue, 8 Feb 2022 17:23:38 GMT, Stuart Marks <smarks at openjdk.org> wrote:

> PR for Sequenced Collections implementation.

src/java.base/share/classes/java/util/LinkedHashMap.java line 384:

> 382:             return this.put(k, v);
> 383:         } finally {
> 384:             putMode = PUT_NORM;

@stuart-marks Would it be an alternative to have an  `internalPut(mode, k, v)` so there is no need to have an internal variable which needs to be read/written multiple time per operation? 🤔

src/java.base/share/classes/java/util/SequencedCollection.java line 93:

> 91:      * underlying collection. Changes to the underlying collection might or might not be visible
> 92:      * in this reversed view, depending upon the implementation.
> 93:      *

@stuart-marks Perhaps an opportunity to spec it so that x == x.reversed().reversed() (i.e. unwrap on double-reverse)?

src/java.base/share/classes/java/util/SequencedCollection.java line 155:

> 153:      */
> 154:     default E getLast() {
> 155:         return this.reversed().iterator().next();

@stuart-marks Are these default implementation expected to be used (actually) in the JDK? From a performance PoV, it might make sense to not have default implementations unless strictly needed, and instead keep the code in the JavaDoc as a guideline for "worst-case" performance profile. 🤔

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PR Review Comment: https://git.openjdk.org/jdk/pull/7387#discussion_r987925904
PR Review Comment: https://git.openjdk.org/jdk/pull/7387#discussion_r986962055
PR Review Comment: https://git.openjdk.org/jdk/pull/7387#discussion_r987216743