How to use generic type in aggregation function

Hi scala-user,

 

I have this aggregation function which will sum all Int input arguments:

case class Seed(var total: Int ) {}

def createSeed = Seed(0)

def sum(seed:Seed, value:Int) = seed.total + value

 

I also want to sum all Double values, so I have to have a new class:

case class Seed(var total: Double ) {}

def createSeed = Seed(0.0)

def sum(seed:Seed, value:Double) = seed.total + value

 

Then, I want to make *Seed * to be generic so that I can reuse it for all numeric types, e.g. int, double, long

case class Seed[T:Numeric](var total: T ) {

  def createSeed()(implicit num: Numeric[T]) = Seed(num.zero)

  def sum(seed:Seed[T], value:T) = seed.total + value

}

 

However, it does not work in my scala 2.9.1.

 

How can I define a generic sum function to calculate any numeric value?

 

David

 

Yinwei David Liu   
Morgan Stanley | Cross-Technology Services   
Kerry Parkside | 1155 Fang Dian Road, Pudong New Area   
201204 Shanghai   
Phone: +86 21 2035-2552   
Yinwei.Liu@MorganStanley.com   
   

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On Wed, Jan 11, 2012 at 08:59, Liu, Yinwei David
wrote:
> Hi scala-user,
>
>
>
> I have this aggregation function which will sum all Int input arguments:
>
> case class Seed(var total: Int ) {}
>
> def createSeed = Seed(0)
>
> def sum(seed:Seed, value:Int) = seed.total + value
>
>
>
> I also want to sum all Double values, so I have to have a new class:
>
> case class Seed(var total: Double ) {}
>
> def createSeed = Seed(0.0)
>
> def sum(seed:Seed, value:Double) = seed.total + value
>
>
>
> Then, I want to make *Seed * to be generic so that I can reuse it for all
> numeric types, e.g. int, double, long
>
> case class Seed[T:Numeric](var total: T ) {
>
>   def createSeed()(implicit num: Numeric[T]) = Seed(num.zero)
>
>   def sum(seed:Seed[T], value:T) = seed.total + value
>
> }
>
>
>
> However, it does not work in my scala 2.9.1.
>
>
>
> How can I define a generic sum function to calculate any numeric value?

Well, there's an ambiguous implicit, but, fixing that, it works for me.

scala> import scala.math.Numeric.Implicits._
import scala.math.Numeric.Implicits._

scala> case class Seed[T:Numeric](var total: T ) {
| def createSeed() = Seed(implicitly[Numeric[T]].zero)
| def sum(seed:Seed[T], value:T) = seed.total + value
| }
defined class Seed

Thanks Daniel, adding * scala.math.Numeric.Implicits._* fixed the issue.

David

-----Original Message-----
From: Daniel Sobral [mailto:dcsobral@gmail.com]
Sent: Wednesday, January 11, 2012 8:35 PM
To: Liu, Yinwei David (ISGT)
Cc: scala-user@googlegroups.com
Subject: Re: [scala-user] How to use generic type in aggregation function

On Wed, Jan 11, 2012 at 08:59, Liu, Yinwei David
wrote:
> Hi scala-user,
>
>
>
> I have this aggregation function which will sum all Int input arguments:
>
> case class Seed(var total: Int ) {}
>
> def createSeed = Seed(0)
>
> def sum(seed:Seed, value:Int) = seed.total + value
>
>
>
> I also want to sum all Double values, so I have to have a new class:
>
> case class Seed(var total: Double ) {}
>
> def createSeed = Seed(0.0)
>
> def sum(seed:Seed, value:Double) = seed.total + value
>
>
>
> Then, I want to make *Seed * to be generic so that I can reuse it for all
> numeric types, e.g. int, double, long
>
> case class Seed[T:Numeric](var total: T ) {
>
> def createSeed()(implicit num: Numeric[T]) = Seed(num.zero)
>
> def sum(seed:Seed[T], value:T) = seed.total + value
>
> }
>
>
>
> However, it does not work in my scala 2.9.1.
>
>
>
> How can I define a generic sum function to calculate any numeric value?

Well, there's an ambiguous implicit, but, fixing that, it works for me.

scala> import scala.math.Numeric.Implicits._
import scala.math.Numeric.Implicits._

scala> case class Seed[T:Numeric](var total: T ) {
| def createSeed() = Seed(implicitly[Numeric[T]].zero)
| def sum(seed:Seed[T], value:T) = seed.total + value
| }
defined class Seed