On Tue, 28 Mar 2023 02:37:22 GMT, Stuart Marks <sma...@openjdk.org> wrote:
>> PR for Sequenced Collections implementation. > > Stuart Marks has updated the pull request incrementally with one additional > commit since the last revision: > > Simplify handling of cached keySet, values, and entrySet views. In the JEP: > A sequenced collection supports common operations at either end, and it > supports processing the elements from first to last and from last to first > (i.e., forward and reverse). > The reverse-ordered view enables all the different sequenced types to process > elements in both directions, using all the usual iteration mechanisms: > Enhanced for loops, explicit iterator() loops, forEach(), stream(), > parallelStream(), and toArray(). This implies that for the reversed view, collection operations are not only supported, but can potentially be optimized. Our design should anticipate implementations of `SequencedCollection` to provide specific reversed implementations, like what we are already doing with `addAll` in ArrayList and ArrayDeque. If a collection cannot have efficient reverse-sequenced operations, it shouldn't be retrofitted into `SequencedCollection`, just like how we don't fit Deques into Lists. Hence, I recommend: 1. Declare `reversed()` and one of the (First/Last) operation sets (add|get|remove) `abstract`, and delegae the other set to default call the operation on the reversed instead. - Since we tend to work with the end of collections, I'd declare the `Last` methods to be abstract and delegate the `First` default implementations to `this.reversed().xxxLast()` 2. I don't think leaving `addLast()` implemented by default is a good idea, for modifiable implementations cannot discover that they missed the `addLast()` at compile time and can only discover when the implementation is actually used. 3. In the default `reversed()` implementation of `List` and `Deque`, add API notes to indicate to implementations opportunities to optimize the implementation, especially batch operations like `addAll` when the base implementation offers such an optimization. ------------- PR Comment: https://git.openjdk.org/jdk/pull/7387#issuecomment-1489338414
