Re: Model abstract class in spark ml

[Cody Koeninger]

http://blog.originate.com/blog/2014/02/27/types-inside-types-in-scala/

On Wed, Aug 31, 2016 at 2:19 AM, Sean Owen  wrote:
> Weird, I recompiled Spark with a similar change to Model and it seemed
> to work but maybe I missed a step in there.
>
> On Wed, Aug 31, 2016 at 6:33 AM, Mohit Jaggi  wrote:
>> I think I figured it out. There is indeed "something deeper in Scala” :-)
>>
>> abstract class A {
>>   def a: this.type
>> }
>>
>> class AA(i: Int) extends A {
>>   def a = this
>> }
>>
>> the above works ok. But if you return anything other than “this”, you will
>> get a compile error.
>>
>> abstract class A {
>>   def a: this.type
>> }
>>
>> class AA(i: Int) extends A {
>>   def a = new AA(1)
>> }
>>
>> Error:(33, 11) type mismatch;
>>  found   : com.dataorchard.datagears.AA
>>  required: AA.this.type
>>   def a = new AA(1)
>>   ^
>>
>> So you have to do:
>>
>> abstract class A[T <: A[T]]  {
>>   def a: T
>> }
>>
>> class AA(i: Int) extends A[AA] {
>>   def a = new AA(1)
>> }
>>
>>
>>
>> Mohit Jaggi
>> Founder,
>> Data Orchard LLC
>> www.dataorchardllc.com
>>
>>
>
> -
> To unsubscribe e-mail: user-unsubscr...@spark.apache.org
>

-
To unsubscribe e-mail: dev-unsubscr...@spark.apache.org

Re: Model abstract class in spark ml

[Sean Owen]

Weird, I recompiled Spark with a similar change to Model and it seemed
to work but maybe I missed a step in there.

On Wed, Aug 31, 2016 at 6:33 AM, Mohit Jaggi  wrote:
> I think I figured it out. There is indeed "something deeper in Scala” :-)
>
> abstract class A {
>   def a: this.type
> }
>
> class AA(i: Int) extends A {
>   def a = this
> }
>
> the above works ok. But if you return anything other than “this”, you will
> get a compile error.
>
> abstract class A {
>   def a: this.type
> }
>
> class AA(i: Int) extends A {
>   def a = new AA(1)
> }
>
> Error:(33, 11) type mismatch;
>  found   : com.dataorchard.datagears.AA
>  required: AA.this.type
>   def a = new AA(1)
>   ^
>
> So you have to do:
>
> abstract class A[T <: A[T]]  {
>   def a: T
> }
>
> class AA(i: Int) extends A[AA] {
>   def a = new AA(1)
> }
>
>
>
> Mohit Jaggi
> Founder,
> Data Orchard LLC
> www.dataorchardllc.com
>
>

-
To unsubscribe e-mail: dev-unsubscr...@spark.apache.org

Re: Model abstract class in spark ml

[Mohit Jaggi]

I think I figured it out. There is indeed "something deeper in Scala” :-)

abstract class A {
  def a: this.type
}

class AA(i: Int) extends A {
  def a = this
}
the above works ok. But if you return anything other than “this”, you will get 
a compile error.

abstract class A {
  def a: this.type
}

class AA(i: Int) extends A {
  def a = new AA(1)
}
Error:(33, 11) type mismatch;
 found   : com.dataorchard.datagears.AA
 required: AA.this.type
  def a = new AA(1)
  ^

So you have to do:

abstract class A[T <: A[T]]  {
  def a: T
}

class AA(i: Int) extends A[AA] {
  def a = new AA(1)
}


Mohit Jaggi
Founder,
Data Orchard LLC
www.dataorchardllc.com




> On Aug 30, 2016, at 9:51 PM, Mohit Jaggi  wrote:
> 
> thanks Sean. I am cross posting on dev to see why the code was written that 
> way. Perhaps, this.type doesn’t do what is needed.
> 
> Mohit Jaggi
> Founder,
> Data Orchard LLC
> www.dataorchardllc.com 
> 
> 
> 
> 
>> On Aug 30, 2016, at 2:08 PM, Sean Owen > > wrote:
>> 
>> I think it's imitating, for example, how Enum is delcared in Java:
>> 
>> abstract class Enum>
>> 
>> this is done so that Enum can refer to the actual type of the derived
>> enum class when declaring things like public final int compareTo(E o)
>> to implement Comparable. The type is redundant in a sense, because
>> you effectively have MyEnum extending Enum.
>> 
>> Java allows this self-referential definition. However Scala has
>> "this.type" for this purpose and (unless I'm about to learn something
>> deeper about Scala) it would have been the better way to express this
>> so that Model methods can for example state that copy() returns a
>> Model of the same concrete type.
>> 
>> I don't know if it can be changed now without breaking compatibility
>> but you're welcome to give it a shot with MiMa to see. It does
>> compile, using this.type.
>> 
>> 
>> On Tue, Aug 30, 2016 at 9:47 PM, Mohit Jaggi > > wrote:
>>> Folks,
>>> I am having a bit of trouble understanding the following:
>>> 
>>> abstract class Model[M <: Model[M]]
>>> 
>>> Why is M <: Model[M]?
>>> 
>>> Cheers,
>>> Mohit.
>>> 
> 

Re: Model abstract class in spark ml

[Mohit Jaggi]

thanks Sean. I am cross posting on dev to see why the code was written that
way. Perhaps, this.type doesn’t do what is needed.

Mohit Jaggi
Founder,
Data Orchard LLC
www.dataorchardllc.com




On Aug 30, 2016, at 2:08 PM, Sean Owen  wrote:

I think it's imitating, for example, how Enum is delcared in Java:

abstract class Enum>

this is done so that Enum can refer to the actual type of the derived
enum class when declaring things like public final int compareTo(E o)
to implement Comparable. The type is redundant in a sense, because
you effectively have MyEnum extending Enum.

Java allows this self-referential definition. However Scala has
"this.type" for this purpose and (unless I'm about to learn something
deeper about Scala) it would have been the better way to express this
so that Model methods can for example state that copy() returns a
Model of the same concrete type.

I don't know if it can be changed now without breaking compatibility
but you're welcome to give it a shot with MiMa to see. It does
compile, using this.type.


On Tue, Aug 30, 2016 at 9:47 PM, Mohit Jaggi  wrote:

Folks,
I am having a bit of trouble understanding the following:

abstract class Model[M <: Model[M]]

Why is M <: Model[M]?

Cheers,
Mohit.

Re: Model abstract class in spark ml

[Mohit Jaggi]

thanks Sean. I am cross posting on dev to see why the code was written that 
way. Perhaps, this.type doesn’t do what is needed.

Mohit Jaggi
Founder,
Data Orchard LLC
www.dataorchardllc.com




> On Aug 30, 2016, at 2:08 PM, Sean Owen  wrote:
> 
> I think it's imitating, for example, how Enum is delcared in Java:
> 
> abstract class Enum>
> 
> this is done so that Enum can refer to the actual type of the derived
> enum class when declaring things like public final int compareTo(E o)
> to implement Comparable. The type is redundant in a sense, because
> you effectively have MyEnum extending Enum.
> 
> Java allows this self-referential definition. However Scala has
> "this.type" for this purpose and (unless I'm about to learn something
> deeper about Scala) it would have been the better way to express this
> so that Model methods can for example state that copy() returns a
> Model of the same concrete type.
> 
> I don't know if it can be changed now without breaking compatibility
> but you're welcome to give it a shot with MiMa to see. It does
> compile, using this.type.
> 
> 
> On Tue, Aug 30, 2016 at 9:47 PM, Mohit Jaggi  wrote:
>> Folks,
>> I am having a bit of trouble understanding the following:
>> 
>> abstract class Model[M <: Model[M]]
>> 
>> Why is M <: Model[M]?
>> 
>> Cheers,
>> Mohit.
>> 


-
To unsubscribe e-mail: dev-unsubscr...@spark.apache.org