I like the idea to support partial functions with Flink’s Scala API. However, I think that breaking the API and making it inconsistent with respect to the Java API is not the best option. I would rather be in favour of the first proposal where we add a new method xxxWith via implicit conversions.
Cheers, Till On Sun, Feb 7, 2016 at 12:44 PM, Stefano Baghino < stefano.bagh...@radicalbit.io> wrote: > It took me a little time but I was able to put together some code. > > In this commit I just added a few methods renamed to prevent overloading, > thus usable with PartialFunction instead of functions: > > https://github.com/radicalbit/flink/commit/aacd59e0ce98cccb66d48a30d07990ac8f345748 > > In this other commit I coded the original proposal, renaming the methods to > obtain the same effect as before, but with lower friction for Scala > developers (and provided some usage examples): > > https://github.com/radicalbit/flink/commit/33403878eebba70def42f73a1cb671d13b1521b5 > > On Thu, Jan 28, 2016 at 6:16 PM, Stefano Baghino < > stefano.bagh...@radicalbit.io> wrote: > > > Hi Stephan, > > > > thank you for the quick reply and for your feedback; I agree with you > that > > breaking changes have to taken very seriously. > > > > The rationale behind my proposal is that Scala users are already > > accustomed to higher-order functions that manipulate collections and it > > would beneficial for them to have an API that tries to adhere as much as > > possible to the interface provided by the Scala Collections API. IMHO > being > > able to manipulate a DataSet or DataStream like a Scala collection > > idiomatically would appeal to developers and reduce the friction for them > > to learn Flink. > > > > If we want to pursue the renaming path, I think these changes (and > porting > > the rest of the codebase, like `flink-ml` and `flink-contrib`, to the new > > method names) can be done in relatively little time. Since Flink is > > approaching a major release, I think it's a good time to consider this > > change, if the community deems it relevant. > > > > While we await for feedback on the proposal, I can start working on both > > paths to see how it would affect the codebase, what do you think? > > > > On Thu, Jan 28, 2016 at 2:14 PM, Stephan Ewen <se...@apache.org> wrote: > > > >> Hi! > >> > >> Would be nice to support that, agreed. > >> > >> Such a fundamental break in the API worries me a bit, though - I would > opt > >> for a non-breaking addition. > >> Wrapping the RichFunctions into Scala functions (which are actually > >> wrapped > >> as rich functions) with implicits seems like a workaround for something > >> that should be very simple. Would probably also cost a bit of > performance. > >> > >> > >> I like the idea of "mapWith(...)" - if that were a simple non overloaded > >> function accepting a Scala function, it should accept case-style > >> functions, > >> right? > >> Simply adding that would probably solve things, but add a second variant > >> of > >> each function to the DataSet. An implicit conversion from DataSet to > >> DataSetExtended (which implements the mapWith, reduceWith, ...) methods > >> could help there... > >> > >> What do you think? > >> > >> Greetings, > >> Stephan > >> > >> > >> On Thu, Jan 28, 2016 at 2:05 PM, Stefano Baghino < > >> stefano.bagh...@radicalbit.io> wrote: > >> > >> > Hello everybody, > >> > > >> > as I'm getting familiar with Flink I've found a possible improvement > to > >> the > >> > Scala APIs: in Scala it's a common pattern to perform tuple extraction > >> > using pattern matching, making functions working on tuples more > >> readable, > >> > like this: > >> > > >> > // referring to the mail count example in the training > >> > // assuming `mails` is a DataSet[(String, String)] > >> > // a pair of date and a string with username and email > >> > val monthsAndEmails = > >> > mails.map { > >> > case (date, sender) => > >> > (extractMonth(date), extractEmail(sender)) > >> > } > >> > > >> > However, this is not possible when using the Scala APIs because of the > >> > overloading of the `map` function in the `DataSet` and `DataStream` > >> classes > >> > (along with other higher-order function such as `flatMap` and > >> `filter`). My > >> > understanding is that the main reason to have two different overloaded > >> > functions is to provide support for `RichFunction`s. > >> > I've found out there has been some interest around the issue in the > >> past ( > >> > [FLINK-1159] <https://issues.apache.org/jira/browse/FLINK-1159>). > >> > In the past couple of days me and my colleague Andrea have tried > several > >> > ways to address the problem, coming to two possible solutions: > >> > > >> > 1. don't overload and use different names, e.g. `map` taking a > Scala > >> > function and `mapWith` taking a Flink MapFunction > >> > 2. keep only the method taking a Scala function (which would be > more > >> > idiomatic from a Scala perspective, IMHO) and providing an implicit > >> > conversion from the Flink function to the Scala function within the > >> > `org.apache.flink.api.scala` package object > >> > > >> > We've also evaluated several other approaches using union types and > type > >> > classes but we've found them to be too complex. Regarding the two > >> > approaches I've cited, the first would imply a breaking change to the > >> APIs, > >> > while the second is giving me a hard time at figuring out some > >> compilation > >> > errors in `flink-libraries` and `flink-contrib` and as we tested it we > >> > found out `RichMapFunction`s lose state (possibly because of the > double > >> > conversion, first to a Scala function, then to a simple > `MapFunction`). > >> > > >> > You can have a look at the code I've written so far here (last 2 > >> commits): > >> > https://github.com/radicalbit/flink/commits/1159 > >> > > >> > We had a little exchange of ideas and thought that the first solution > >> would > >> > be easier and also interesting from the standpoint of the ergonomics > of > >> the > >> > API (e.g. `line mapWith new LineSplitter`) and would like to gather > some > >> > feedback on the feasibility of this change. > >> > > >> > Would this still be regarded as a relevant improvement? What do you > >> think > >> > about it? Do you think there's time to work on them before the 1.0 > >> release? > >> > What do you think about introducing breaking changes to make this > >> pattern > >> > available to Scala users? > >> > > >> > Thank you all in advance for your feedback. > >> > > >> > -- > >> > BR, > >> > Stefano Baghino > >> > > >> > Software Engineer @ Radicalbit > >> > > >> > > > > > > > > -- > > BR, > > Stefano Baghino > > > > Software Engineer @ Radicalbit > > > > > > -- > BR, > Stefano Baghino > > Software Engineer @ Radicalbit >
