+1 On Thu, Dec 8, 2016 at 1:10 PM Jean-Baptiste Onofré <j...@nanthrax.net> wrote:
> +1 > > Regards > JB > > On 12/07/2016 10:37 PM, Kenneth Knowles wrote: > > Hi all, > > > > I want to bring up another major backwards-incompatible change before it > is > > too late, to resolve [BEAM-438]. > > > > Summary: Leave PInput.apply the same but rename PTransform.apply to > > PTransform.expand. I have opened [PR #1538] just for reference (it took > 30 > > seconds using IDE automated refactor) > > > > This change affects *PTransform authors* but does *not* affect pipeline > > authors. > > > > This issue was filed a long time ago. It has been a problem many times > with > > actual users since before Beam started incubating. This is what goes > wrong > > (often): > > > > PCollection<Foo> input = ... > > PTransform<PCollection<Foo>, ...> transform = ... > > > > transform.apply(input) > > > > This type checks and even looks perfectly normal. Do you see the error? > > > > ... what we need the user to write is: > > > > input.apply(transform) > > > > What a confusing difference! After all, the first one type-checks and the > > first one is how you apply a Function or Predicate or > SerializableFunction, > > etc. But it is broken. With transform.apply(input) the transform is not > > registered with the pipeline at all. > > > > We obviously can't (and don't want to) change the most core way that > > pipeline authors use Beam, so PInput.apply (aka PCollection.apply) must > > remain the same. But we do need a way to make it impossible to mix these > up. > > > > The simplest way I can think of is to choose a new name for the other > > method involved. Users probably won't write transform.expand(input) since > > they will never have seen it in any examples, etc. This will just make > > PTransform authors need to do a global rename, and the type system will > > direct them to all cases so there is no silent failure possible. > > > > What do you think? > > > > Kenn > > > > [BEAM-438] https://issues.apache.org/jira/browse/BEAM-438 > > [PR #1538] https://github.com/apache/incubator-beam/pull/1538 > > > > p.s. there is a really amusing and confusing call chain: > PCollection.apply > > -> Pipeline.applyTransform -> Pipeline.applyInternal -> > > PipelineRunner.apply -> PTransform.apply > > > > After this change and work to get the runner out of the loop, it becomes > > PCollection.apply -> Pipeline.applyTransform -> PTransform.expand > > > > -- > Jean-Baptiste Onofré > jbono...@apache.org > http://blog.nanthrax.net > Talend - http://www.talend.com >
