Hello, Remi! On Sat, Apr 17, 2021 at 11:50 PM Remi Forax <fo...@univ-mlv.fr> wrote: > Introducing a new interface (two in this case) has a really huge cost and in > this case, i've trouble to see why i will want to write a method that takes a > ReversibleCollection as parameter, ReversibleCollection as a type does not > seem to be useful. About the cost of introducing a new collection interface, > it means that we also have to update all emptyXXX, singleXXX, uncheckedXXX > with a new interface, and that only for the JDK. Every libraries that proxy > collections has also to be updated to take care of this new type, otherwise > the integration with an application that uses this new type and the library > is not seamless anymore.
Note that in Stuart's proposal, java.util.List extends ReversibleCollection. So, existing emptyList() and singletonList() also return ReversibleCollection and no new methods are necessary here. Probably unmodifiableReversibleSet could be useful as a LinkedHashSet wrapper. On the other hand, we don't have, e.g. checkedDeque or synchronizedDeque, and it looks like nobody complains. So probably it's not always necessary to create a wrapper for every single collection interface. > I fully agree that having a way to reverse a collection is a powerful API > point, as Brian said, it's better to reverse the collection and then ask for > a stream than providing a method reverseStream (and this is true for > iterators or views like keySet/entrySet/values or subList too). Several > people also ask to have findLast() on Stream, using > list.descendingList().findFirst() will be equivalent. A dedicated findLast() would be a great addition to reversible streams! It could short-circuit for reversible stream (reverse().findFirst()) and use reduce((a, b) -> b) for non-reversible (so intermediate buffering is not necessary). I've found 8 Stream API call chains ending with .reduce((a, b) -> b) in our sources. Clearly, some of them could short-circuit, as the source is potentially reversible (e.g. allAnchors.subList(0, idx).stream().filter(hasNewName).reduce((x1, x2) -> x2)). Having dedicated findLast operation would be less error-prone, compared to creating the stream as reversed().stream(), as you don't have to think whether the stream is reversible or not. If you accidentally add a non-reversible operation, you'll miss the optimization but not correctness. With best regards, Tagir Valeev.
