dynamic mixin?

Thanks for the reply

1. unimportant: I don’t see a value to use that " self:EntityDef =>" stuff in each class. Extending AspektMath with EntityDef only one time works well:

trait EntityDef { // Interface
 def x:Double
 def y :Double
}

trait Data extends EntityDef{ // Data Implementation
 var y:Double=4
 val x:Double=5
}

trait AspektMath extends EntityDef{ // Functions without Data

 def doMath()
}

trait div extends AspektMath {

 def doMath(){println(x/y)}
}

trait mul extends AspektMath {
 def doMath(){println(x*y)}
}

class Entity extends Data with mul
class Entity2 extends Data with div

But since I don’t have any experience with scala there any benefits for "self:EntityDef" over an extention? Which?

2. unfortunately your suggestion ist not realy a runtime mixin. I could perfectly use that code for the single polymorphism as in my simple example. But in the end I want to have a much more complex Entity with polymorphisms on many aspect like

class Entity extends Data with AspektMath1 with AspektMath2 with AspektMath3 with AspektMath4

each AspektMath1.. AspektMath4 does have a polymorphism and I don’t want to declare the cross-Product of all possible combinations since that may be thousands and due to correlations only a few may be actually used.

Further ideas?

-----Ursprüngliche Nachricht-----
Von: Johannes Rudolph [mailto:johannes.rudolph@...]
Gesendet: Donnerstag, 5. November 2009 10:43
An: Kubitz, Jörg
Cc: scala-user@...
Betreff: Re: [scala-user] dynamic mixin?

Perhaps this way:

trait EntityDef { // Interface
  def x:Double
  def y :Double
}

trait Data extends EntityDef{ // Data Implementation
  var y:Double=4
  val x:Double=5
}

trait AspektMath { // Functions without Data
  def doMath()
}

trait div extends AspektMath {self:EntityDef => // the self type
ensures that this trait can
                                                                   //
only be mixed if EntityDef is mixed in as well
  def doMath(){println(x/y)}
}

trait mul extends AspektMath {self:EntityDef =>
  def doMath(){println(x*y)}
}

trait Entity extends Data with mul
trait Entity2 extends Data with div

etc.

--
Johannes

-----------------------------------------------
Johannes Rudolph
http://virtual-void.net

Hi,

 

i am new to scala and want to understand how I could use scalas traits.

I’d like to have something like a dynamic mixin i.e. I know wich which trait-hirarchie I want to mix in  at compile time but don’t know which actual Trait I want to use at runtime.

I know that I could do it in java with the Strategy-Pattern, but I thought traits could help me with it. But it doesn’t seem to work:

 

 

trait EntityDef { // Interface

  def x:Double

  def y :Double

}

 

trait Data extends EntityDef{ // Data Implementation

  var y:Double=4

  val x:Double=5

}

 

trait AspektMath extends EntityDef { // Functions without Data

  def doMath()

}

 

trait div extends AspektMath {

  def doMath(){println(x/y)} 

}

trait mul extends AspektMath {

  def doMath(){println(x*y)}

}

 

trait  Entity[T >: AspektMath] extends Data with T {

  //does not compile

}

 

 

Any suggestions?

 

 

Dr. Jörg Kubitz
________________________________________
zeb/information.technology gmbh & co. kg

Hammer Straße 165
48153 Münster

Phone	+4925197128-567
Fax	+4925197128-101
E-Mail	jkubitz@...
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Geschäftsführer: Martin Danne | Jürgen Hofner | Andreas Schick

 

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Hi Stefan,

 

“Object with mul” does not compile since x,y are not defined.

But “Data with mul” does compile J

 – but it does not calculate the desired result L since the wrong (default) datas are mixed in.

I would need to mix in an existing object like “=d with mul”

 

trait EntityDef1 { // Interface1

  def x:Double

}

 

trait EntityDef2 extends EntityDef1 { // Interface2

  def y:Double

}

 

class Data extends EntityDef2{ // Data Implementation

  var y:Double=4

  var x:Double=5

}

 

trait AspektMath1 extends EntityDef1 { // Functions with 1 parameter without data

  def doMath1()

}

trait log extends AspektMath1 {

  def doMath1(){println(Math.log(x))} 

}

trait exp extends AspektMath1 {

  def doMath1(){println(Math.exp(x))}

} 

 

trait AspektMath2 extends EntityDef2 { // Functions with 2 parameters without data

  def doMath2()

}

trait div extends AspektMath2 {

  def doMath2(){println(x/y)} 

}

trait mul extends AspektMath2 {

  def doMath2(){println(x*y)}

}

 

class  Entity(math1: AspektMath1,math2: AspektMath2) extends Data with AspektMath1 with AspektMath2{

    def doMath1=math1.doMath1

    def doMath2=math2.doMath2

}

 

class c1 {

//  var d:Data= new Data

//  d.x=10

//  d.y=20

  var m1:AspektMath1 =new Data with exp

  var m2:AspektMath2 =new Data with mul

  var e=new Entity(m1, m2)

  e.x=10

  e.y=20

  e.doMath1  // gives exp(5)=148.4131591025766 // should be exp(10) = 22026,4657948067

  e.doMath2  // gives 4*5=20 // should be 10*20 = 200

}

 

Von: Stefan Langer [mailto:mailtolanger@...]
Gesendet: Donnerstag, 5. November 2009 11:17

An: Kubitz, Jörg
Cc: scala-user@...
Betreff: Re: [scala-user] dynamic mixin?

 

Danymic mixins are not supported directly.

You are basically trying to mixin a trait on an existing object? If you are not interested to mix into an existing object
you can use pattern matching on the type to get what you want

Soemthing along the lines
getMixin[T :< AspektMath](a: T) = {
      a: Multi => new Object with mul
      a: Div => new Object with div
}

or you use getMixin[ T <% AspektMath](a: T) = ...
then you need to provide an implict that is capable of turning T into a type of AspektMath.

This is just an idea that I haven't tested since I do not have access to a scala shell at this computer.

Regards
Stefan

2009/11/5 Kubitz, Jörg <jkubitz@...>

Thanks for the reply

1. unimportant: I don’t see a value to use that " self:EntityDef =>" stuff in each class. Extending AspektMath with EntityDef only one time works well:

trait EntityDef { // Interface
 def x:Double
 def y :Double
}

trait Data extends EntityDef{ // Data Implementation
 var y:Double=4
 val x:Double=5
}

trait AspektMath extends EntityDef{ // Functions without Data

 def doMath()
}

trait div extends AspektMath {

 def doMath(){println(x/y)}
}

trait mul extends AspektMath {
 def doMath(){println(x*y)}
}

class Entity extends Data with mul
class Entity2 extends Data with div

But since I don’t have any experience with scala there any benefits for "self:EntityDef" over an extention? Which?

2. unfortunately your suggestion ist not realy a runtime mixin. I could perfectly use that code for the single polymorphism as in my simple example. But in the end I want to have a much more complex Entity with polymorphisms on many aspect like

class Entity extends Data with AspektMath1 with AspektMath2 with AspektMath3 with AspektMath4

each AspektMath1.. AspektMath4 does have a polymorphism and I don’t want to declare the cross-Product of all possible combinations since that may be thousands and due to correlations only a few may be actually used.

Further ideas?

-----Ursprüngliche Nachricht-----
Von: Johannes Rudolph [mailto:johannes.rudolph@...]
Gesendet: Donnerstag, 5. November 2009 10:43
An: Kubitz, Jörg
Cc: scala-user@...
Betreff: Re: [scala-user] dynamic mixin?

Perhaps this way:

trait EntityDef { // Interface
  def x:Double
  def y :Double
}

trait Data extends EntityDef{ // Data Implementation
  var y:Double=4
  val x:Double=5
}

trait AspektMath { // Functions without Data
  def doMath()
}

trait div extends AspektMath {self:EntityDef => // the self type
ensures that this trait can
                                                                   //
only be mixed if EntityDef is mixed in as well
  def doMath(){println(x/y)}
}

trait mul extends AspektMath {self:EntityDef =>
  def doMath(){println(x*y)}
}

trait Entity extends Data with mul
trait Entity2 extends Data with div

etc.

--
Johannes

-----------------------------------------------
Johannes Rudolph
http://virtual-void.net