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From Naveen Swamy <>
Subject Re: Feedback request for new Java API
Date Sat, 29 Sep 2018 19:05:05 GMT
I know it is about trade-off.  I am suggesting a trade-off , how many apis do we have that
takes too many parameters ? 
From what I recall its around 20. Why can we not create the builder just for these APIs( which
we discussed), why is it necessary to add 200 Apis ?
Are you suggesting to create builder for each and every API?

I disagree with your opinion that they are not important and would like to hear from others.

I am curious to see how the #2 looks like compared to #1 
Andrew/Qing, can you paste the generated Apis that you have for both Scala and Java in a gist

> On Sep 29, 2018, at 2:41 PM, YiZhi Liu <> wrote:
> Naveen, software designing is all about tradeoff, every feature we
> introduce causes more compiling time, more efforts to maintain, etc.
> The main difference is.
> Option #1: Java users do
> NDArray.BatchNorm(data, gamma, beta, null, null, null, null, null,
> null, null, null, null, null, null);
> (and because every operator has an argument "out", users need to add
> an extra "null" to the function call almost every time.)
> Option #2, Java users do
> JavaNDArray.BatchNorm(data).setGamma(gamma).setBeta(beta).invoke();
> I don't think any of the reasons you listed is so important as the
> benefit above we got from option #2.
>> On Sat, Sep 29, 2018 at 8:24 AM Naveen Swamy <> wrote:
>> Java APIs are not like Clojure - The current proposal is only to build a
>> few thin wrappers for Inference.
>> To better represent the two cases and this discussion in particular, here
>> is an example API
>> 1) def Activation (data : org.apache.mxnet.NDArray, act_type : String, out
>> : Option[NDArray] = None) : org.apache.mxnet.NDArrayFuncReturn
>> or
>> 2) def Activation (data : org.apache.mxnet.NDArray, act_type : String, out
>> : NDArray) : org.apache.mxnet.NDArrayFuncReturn
>> The discussion is should we add(generate) 200+ APIs to make it Java
>> compatible, ie., remove the Option class and the None default value which
>> Java does not understand from Option 1)
>> my suggestion was to remove the Option class and create a implicit for
>> backward compatibility and use null instead of None, Andrew and I disagreed
>> on this, so I suggested to raise a discussion on dev@ to get more opinions
>> and one of us will disagree and commit. Thanks for raising it :)
>> | * def Activation (data : org.apache.mxnet.NDArray, act_type : String, out
>> : NDArray = null) : org.apache.mxnet.NDArrayFuncReturn |
>> --
>> 1) It is not true that Scala users will lose *default/optional* arguments -
>> if we followed the above, they will use null or None, though I do not like
>> using nulls, this is a fine compromise.
>> To keep backward compatibility we can create a implicit to convert
>> Option.None to nulls and Option.Some-> Option.get(), so you are not going
>> to break users who might have been using the APIs that were released in
>> 1.3. The current incompatibility is only this w.r.t. NDArrays.
>> 2) Now about the Scala Macros - they are not simple to read or use, When I
>> and Qing started working on the #Scala Macros to improve the APIs, it took
>> us a good amount of time to get a hang of it. I don't want to add
>> additional code when not necessary.
>> My suggestion and vote is to modify existing Macro(i.e., #1 from the
>> original email with the necessary clarification above) and make it
>> compatible with Java
>> Here are my reasons
>> 1) The NDArray APIs in question are not following functional style of
>> programming, in fact they are just static methods defined on an NDArray
>> object - so Scala users are not losing much by using null in place of None.
>> You can create a implicit to maintain backward compatibility
>> 2) It is adding 220+ APIs(I understand it is generated) for NDArray alone
>> 3) this is adding another 100s of APIs unnecessarily, we are starting with
>> NDArray but we can't stop there, we will have to do this for Symbol,
>> Executor, Iterators, etc., .
>> 3) I don't want to be fixing bugs and maintaining code in 2 places.
>> 4) I want the cryptic code(# scala macros) to a minimum.
>> 5) increased compilation time & bad developer experience - the time to
>> compile has gone up quite a bit since we added the APIs last release on my
>> 3 year old laptop already.. I think adding 400+ APIs unnecessarily would
>> significantly increase build time and bad developer experience
>> 6) I want to keep the core of the framework to be in Scala - because it
>> allows you to write concise code - Yes it has a bit of learning curve, not
>> everyone needs to know. I would rather invest in solidifying the Scala APIs
>> and add more features in Scala(RNN, Support GluonHybridizedBlock...there is
>> quite bit of work ) - do you want to rewrite everything in Scala and Java.
>> 7) Also, the discussion is not creating NDArray class for Java, just
>> generate certain APIs to cater for Java incompatibility.
>> @Andrew: To your response to Qing's comments - you cannot just consider it
>> as just generating NDArray's APIs and instead I suggest to take a wholistic
>> view of all the various implications.
>> @Chris: Yes, Scala has a bit of learning curve - the goal is not having
>> every developer to deal with how these APIs are generated,
>> the problem exists either ways with the above proposal. I might agree if we
>> were to move away completely(with a thorough discussion and valid reasons)
>> and instead use AspectJ or similar to write these APIs, the discussion is
>> about using Scala Macros to generate 2 different types of APIs which are
>> functionally not different and usability wise are very very similar, look
>> at the example.
>> Thanks for your input, I will deposit your 0.02$ in our JIRA bank :)
>> @Carin: It requires more effort to use AspectJ or similar to generate APIs
>> using reflection or at compile time, here we need to generate at compile
>> time so Java users have the API signature on their IDEs.
>> Thanks, Naveen
>> P.S: I am traveling and my responses will be delayed.
>>> On Fri, Sep 28, 2018 at 10:25 AM Carin Meier <> wrote:
>>> Sorry bad paste on the gist - here is the good one
>>>> On Fri, Sep 28, 2018 at 10:24 AM Carin Meier <>
>>>> +1 on option #2
>>>> In the case of minimizing the the overhead for code maintenance, I wanted
>>>> to suggest the option of investigating generating code from the Java
>>>> Reflection for the Java APIs.  I did a quick gist from Clojure of what
>>> the
>>>> generated classes look like from the current Scala Symbol.api for
>>>> FullyConnected here
>>>> I looks like that there is always a base Java class generated will all
>>> the
>>>> arguments. If this is the case, then there is a possibility to generate a
>>>> Java api based on this Java method automatically with just a conversion
>>> for
>>>> the Scala option and it might be reusable for all the packages.
>>>> Not sure if it will work for this use case, but thought I would bring it
>>>> up in case it's helpful.
>>>> - Carin
>>>> On Fri, Sep 28, 2018 at 7:05 AM Davydenko, Denis <
>>>> wrote:
>>>>> +1 on option #2. Having clear Java interface for NDArray, from my
>>>>> perspective, would be a better experience for Java users as it won't
>>>>> require them to deal with Scala code in any capacity. Overhead of extra
>>>>> code for additional macros is justified, in my mind, as it will be
>>>>> introduced with option #1 either way, just in a different place.
>>>>> --
>>>>> Thanks,
>>>>> Denis
>>>>> On 9/27/18, 6:14 PM, "YiZhi Liu" <> wrote:
>>>>>  I vote for "2.) Leave the existing macro in place and add another
>>>>>  which generates a Java friendly version"
>>>>>  @Qing @Andrew, could you give some examples, so that people can
>>> better
>>>>>  understand how it provides "best possible experience" to Java users.
>>>>>  I have no strong preference between having JavaShape & JavaContext
>>> or
>>>>> not.
>>>>>  On Thu, Sep 27, 2018 at 5:56 PM Andrew Ayres <
>>>>>> wrote:
>>>>>> That's not really the conversation I'm wanting to have. I want a
>>>>> discussion
>>>>>> about the macros with respect to NDArray so that we can get
>>>>> agreement on
>>>>>> our path forward with respect to implementing the NDArray wrapper.
>>>>>> The design that was put forth and agreed to was for a a Java
>>>>> wrapper around
>>>>>> the Scala API. Adding a bunch of Java friendly methods inside the
>>>>> Scala
>>>>>> code would create a mess for users. Maintenance would be
>>>>> essentially the
>>>>>> same for both because either way you're going to be updating Java
>>>>> methods
>>>>>> when you make Scala changes.
>>>>>> Let's please stick with the issue in the original email.
>>>>>> Thanks,
>>>>>> Andrew
>>>>>>> On Thu, Sep 27, 2018 at 5:22 PM Qing Lan <>
>>>>>> wrote:
>>>>>>> I would like to loop this back a layer. Current, there is a
>>>>> discussion in
>>>>>>> the MXNet Scala community on the ways to implement the Java
>>> APIs.
>>>>> Currently
>>>>>>> there are two thoughts:
>>>>>>> 1. Make Scala Java Friendly (Create Java compatible methods in
>>>>> the Scala
>>>>>>> Class. such as NDArray with Java compatible constructor)
>>>>>>> 2. Make Java friendly wrappers in Scala (Andrew's explanation
>>>>> below)
>>>>>>> The first approach require minimum input from our side to
>>>>> implement
>>>>>>> however bring user a bunch of useless api they may not want to
>>>>> use. It also
>>>>>>> makes Scala package heavier. The good thing is these two
>>> packages
>>>>> require
>>>>>>> minimum maintenance cost. As a tradeoff, if any time in the
>>>>> future we want
>>>>>>> to make Java big (make Java as the primary language supported
>>>>> MXNet),
>>>>>>> then the migration from Scala to Java will be harmful. Spark
>>>>> consider this
>>>>>>> carefully and decide not to change much on their Scala code base
>>>>> to make it
>>>>>>> more Java.
>>>>>>> The second approach will make unique NDArray, Shape, Context
>>>>> more. The
>>>>>>> good thing about this is we can always holds a version control
>>> on
>>>>> Java.
>>>>>>> Some breaking changes on Scala may not influence much on Java.
>>> It
>>>>> did the
>>>>>>> best way to decouple the module and good for us to build unique
>>>>> pipeline
>>>>>>> for Java. The bad thing with this design is the maintenance cost
>>>>> as we need
>>>>>>> to keep two code bases, but it also make Java side easy to
>>> change
>>>>> to make
>>>>>>> it better compatible with users.
>>>>>>> Thanks,
>>>>>>> Qing
>>>>>>> On 9/27/18, 3:25 PM, "Andrew Ayres" <>
>>>>> wrote:
>>>>>>>  Hi,
>>>>>>>  Currently, we're working to implement a new Java API and
>>>>> would like
>>>>>>> some
>>>>>>>  feedback from the community on an implementation detail. In
>>>>> short, the
>>>>>>> new
>>>>>>>  Java API will use the existing Scala API (in a manner
>>> similar
>>>>> to how
>>>>>>> the
>>>>>>>  current Clojure API works). This basically means that we're
>>>>> making Java
>>>>>>>  friendly wrappers to call the existing Scala API.
>>>>>>>  The feedback we're looking for is on the implementation of
>>>>> NDArray.
>>>>>>> Scala's
>>>>>>>  NDArray has a significant amount of code which is generated
>>>>> via macros
>>>>>>> and
>>>>>>>  we've got two viable paths to move forward:
>>>>>>>  1.) Change the macro to generate Java friendly methods  - To
>>>>> do this
>>>>>>> we'll
>>>>>>>  modify the macro so that the generated methods won't have
>>>>>>> default/optional
>>>>>>>  arguments. There may also have to be some changes to
>>>>> parameter types to
>>>>>>>  make them Java friendly. The big advantage here is that
>>>>> ongoing
>>>>>>> maintenance
>>>>>>>  will easier. The disadvantages are that we'll be changing
>>> the
>>>>> existing
>>>>>>>  Scala NDArray Infer API (it's marked experimental) and Scala
>>>>> users will
>>>>>>>  lose the ability to use the default and optional arguments.
>>>>>>>  2.) Leave the existing macro in place and add another which
>>>>> generates a
>>>>>>>  Java friendly version - The biggest issue here is that we'll
>>>>> be
>>>>>>> doubling
>>>>>>>  the number of macros that we've got to maintain. It'll
>>> become
>>>>> even more
>>>>>>>  overhead once we start expanding the Java API with more
>>>>> classes that
>>>>>>> use
>>>>>>>  generated code like this. The advantages are that the
>>>>> existing Scala
>>>>>>>  NDArray Infer API would remain unchanged for Scala users and
>>>>> that the
>>>>>>> new
>>>>>>>  macro could be optimized to give the best possible
>>> experience
>>>>> to the
>>>>>>> Java
>>>>>>>  API.
>>>>>>>  Thanks,
>>>>>>>  Andrew
>>>>>  --
>>>>>  Yizhi Liu
>>>>>  DMLC member
>>>>>  Amazon Web Services
>>>>>  Vancouver, Canada
> -- 
> Yizhi Liu
> DMLC member
> Amazon Web Services
> Vancouver, Canada

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