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From Qing Lan <lanking...@live.com>
Subject Re: The New Scala API
Date Wed, 02 May 2018 18:57:07 GMT
Hi Pedro,

Thanks for your comments!

For the first one: please see the definition for attr here: https://mxnet.incubator.apache.org/api/python/symbol/symbol.html?highlight=attr#mxnet.symbol.Symbol.attr.
It is a user defined Struct.  Our old API indeed using null instead of Option + None configuration
and the new API will go Option + None.

For Second one, the new API provide the type for attribute: 
e.g: def Activation(data : Option[Symbol], act_type : String, name : Option[String], attr
: Option[Map[String, String]])
def Pad(data : Option[Symbol] = None, mode : String, pad_width : Shape, constant_value : Option[Double]
= None, name : Option[String] = None, attr : Option[Map[String, String]] = None)
And you are right, that's exactly we are working on now, make a parser for Scala to C++ Type,
see here: 
https://github.com/lanking520/incubator-mxnet/blob/scala-macros-impl/scala-package/macros/src/main/scala/org/apache/mxnet/SymbolMacro.scala#L147

Thanks,
Qing

On 5/2/18, 3:50 AM, "Pedro Larroy" <pedro.larroy.lists@gmail.com> wrote:

    Hi
    
    I had a brief look and I have some comments:
    
    1 - Excessive use of Option: Having an optional map is often not necessary.
    What's the semantic difference between an empty map and passing None? What
    about a variable argument list of Pairs like:
    
    (attr: Pair[String,Sring]*)     it can be then called like ("lr" -> "0.01",
    "activation" -> "relu")   with variable number of arguments.
    
    null is definitely bad, but we can have an empty map or other default
    arguments that make sense in some cases, like an empty string for name
    instead of an optional string. I'm very much pro Option instead of null but
    it adds clunkiness that is not always necessary, as explained.
    
    2 - One of the fundamental problems is that the arguments are untyped, of
    type String -> String, I don't see this solved in this proposal. Is it
    possible to do something better, ie. have typed arguments? when we extend
    dmlc::Parameter we actually know the C++ type, we could do something smart
    about this. For example using clang to extract the types and generate the
    API with proper types.
    
    
    Pedro.
    
    On Wed, May 2, 2018 at 4:01 AM, Naveen Swamy <mnnaveen@gmail.com> wrote:
    
    > No, the implementation still comes from MXNet backend.
    > I don't think there would be any overhead unlike C++ with virtual
    > functions, Interface or trait is just telling you what the signature looks
    > like. users program against interfaces and can choose a different
    > implementation if they like. For example(only to explain the topic) if we
    > had different implementations for CPU and GPU, they could simply choose the
    > version of Implementation they like. To visualize think of a bridge design
    > pattern.
    >
    >
    >
    > On Tue, May 1, 2018 at 6:49 PM, Marco de Abreu <
    > marco.g.abreu@googlemail.com
    > > wrote:
    >
    > > Hey Naveen,
    > >
    > > I'm not familiar with Scala, so please correct me if I'm wrong with my
    > > assumptions. This basically sounds like we'd have an interface for the
    > > Scala API and a separate implementation, right?
    > >
    > > In general, I really like these decoupled approaches (you already
    > > highlighted the advantages)! It would introduce a small overhead since
    > we'd
    > > have to define the traits and implementation at two (different)
    > locations,
    > > but it definitely increases clarity and separates concerns. I don't think
    > > we will have multiple implementations in future, but this might allow us
    > to
    > > define the user-facing API in form of traits while allowing us to change
    > > the underlying "glue" as we want.
    > >
    > > My only slight concern is that this would introduce a bit more overhead
    > > since the documentation and API are defined somewhere else, but I have no
    > > experience with Scala, so I'll leave this up to the people who are more
    > > familiar with the topic.
    > >
    > > Best regards,
    > > Marco
    > >
    > > On Tue, May 1, 2018 at 11:48 PM, Naveen Swamy <mnnaveen@gmail.com>
    > wrote:
    > >
    > > > I think this project is going to significantly improve the usability of
    > > > MXNet-Scala APIs.
    > > >
    > > > I had a offline discussion with Qing about this. I agree with Yizhi
    > that
    > > > keeping in the same namespace will make it easy for existing and new
    > > users
    > > > to quickly lookup the APIs. Along with that I have one recommendation,
    > > > first generate a trait for all the APIs and have the the instance in
    > the
    > > > existing symbol. The usage would be something like below:
    > > >
    > > > trait SymbolAPIBase {
    > > > /**
    > > > api doc
    > > > */
    > > > def Activation()
    > > > }
    > > >
    > > > object SymbolAPI extends SymbolAPIBase {
    > > > def Activation()
    > > > }
    > > >
    > > > object Symbol {
    > > >  val api: SymbolBase = new SymbolAPI()
    > > > }
    > > >
    > > > Now users would use it as
    > > > Symbol.api.Activation()
    > > >
    > > > Creating a trait/Interface as several advantages:
    > > > 1) User do not have to know which concrete class to use, can be decided
    > > > later(Dependency Injection or Configuration driven application)
    > > > 2) Easier to change the implementation later without breaking the user
    > > code
    > > > -> You can insert different implementations through configuration using
    > > > frameworks such as Spring, etc., -> This is standard in most JVM driven
    > > > projects
    > > > 3) Easier to Unit test -> You can create Mocks easily using Mockito
    > > > 4) helps with multiple inheritance…you cannot inherit multiple classes
    > > >
    > > > Let me know what do you guys think.
    > > >
    > > > Thanks, Naveen
    > > >
    > > > On Sun, Apr 22, 2018 at 9:09 PM, YiZhi Liu <liuyizhi@apache.org>
    > wrote:
    > > >
    > > > > I personally like the design here. Since we have seen technical
    > > > > difficulties of compatibility, I would like to ask people pay
    > > > > attention to the 'How to combine with existing APIs' section:
    > > > > https://cwiki.apache.org/confluence/display/MXNET/
    > > > > MXNet+Scala+API+Usability+Improvement#MXNetScalaAPIUsabilityImprovem
    > > ent-
    > > > > HowtocombinewithexistingAPIs
    > > > >
    > > > > Qing proposed three options,
    > > > >
    > > > > 1. Add a new Class/Object called "NewSymbol/NDArray" with full
    > > > > implementation.
    > > > > 2. Create a new Class and change the name space for all of the
    > > > > functions (e.g Activation -> NewActivation) and let Symbol/NDArray
    > > > > extends that.
    > > > > 3. Create a new Class and override the Same functions with different
    > > > > implementations.
    > > > >
    > > > > If we have to choose from option 1 and 2, I would like to +0.5 for
    > > > > option 2, with which users can quickly aware of the new easy-to-use
    > > > > API: they type 'Symbol.' in IDE as usual and these functions pop up.
    > > > >
    > > > > 2018-04-19 10:58 GMT-07:00 Qing Lan <lanking520@live.com>:
    > > > > > Hi All,
    > > > > >
    > > > > > I am Qing, one of the Scala API maintainer for MXNet. I would
like
    > to
    > > > > propose a new design on Scala APIs, it will be really helpful for
    > user
    > > to
    > > > > use MXNet Symbol/NDArray. This is a follow-up from Naveen’s proposal.
    > > > > >
    > > > > > Background:
    > > > > > The current design on Scala would take arguments as key-value
pair
    > > and
    > > > > didn’t provide the type information for different arguments. There
    > are
    > > > > document missing for different functions which makes it even hard
to
    > > use.
    > > > > >
    > > > > > Our approach:
    > > > > > We will provide a better designed Scala API for user to use with
    > full
    > > > > documentation and arguments definition. All arguments will be
    > > > specifically
    > > > > targeted to different functions. Please see one example that we show
    > in
    > > > the
    > > > > Wiki<https://cwiki.apache.org/confluence/display/MXNET/
    > > > > MXNet+Scala+API+Usability+Improvement> and leave any thoughts you
    > may
    > > > > have. This wiki includes examples, targets and scenarios we have so
    > > far.
    > > > > >
    > > > > > Thanks,
    > > > > > Qing
    > > > >
    > > > >
    > > > >
    > > > > --
    > > > > Yizhi Liu
    > > > > DMLC member
    > > > > Amazon Web Services
    > > > > Vancouver, Canada
    > > > >
    > > >
    > >
    >
    

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