> From: "Rafael Winterhalter" <rafael....@gmail.com> > To: "core-libs-dev" <core-libs-...@openjdk.java.net> > Sent: Thursday, January 16, 2025 8:13:17 AM > Subject: Factory methods for SequencedSet and SequencedMap
> Hello, Hello, > I am happily taking SequencedSet and SequencedMap into use, but one > inconvenience I encounter is the lack of factory methods for the two. > In code where many (initial) collections have zero or one element (for later > aggregation), I now write Set.of()/Set.of(one) and Map.of()/Map.of(key, > value), > as it makes the code shorter and more readable. Those collections are of > course > implicitly sequenced, but now I must make the variable type of the surrounding > monad Set and Map, and simply assume that a LinkedHashSet or LinkedHashMap is > used when a collection of more than one element is set, without requiring the > interface type. This does not require any type casting, as I rely on the > iteration order only, but the code loses some of its expressiveness. > I did not find any discussion around introducing factories for > SequencedSet.of(...) and SequencedMap.of(...), similar to those that exist in > the Set and Map interfaces. Was this ever considered, and if not, could it be? Thanks for re-starting that discussion, it was talked a bit, but not as it should be. So the issue is that currently we do not have any compact, unmodifiable and ordered Set/Map implementation, one use case is when you have data that comes from a JSON object as a Map and you want to keep the inserted order, if by example the JSON is a config file editable by a human, an other example is in unit tests where you want to help the dev to read the output of the test so the code that creates a Set/Map and what is outputed by the test should be in the same order. Currently there is no good solution for those use cases because Set|Map.copyOf() does not keep the ordering. I see two solutions, either we add a new SequenceSet|SequenceMap.of/copyOf, or we change the impleemntation of Set|Map.of()/copyOf(). Python had gone for the latter solution, which has the advantage a being simple from the user POV, but from an algorithm expert POV, a Set and a SequencedSet are different concepts we may want to emphasis ? > Best regards, Rafael regards, Rémi
