how to call super class's contructor

[Zemian Deng]

hello list,

Is there a super() method in Scala that I can do things like this?

class A(x:Int){
    override def toString={x.toString}
}
class B extends A(0) {
  def this(s:String)={
      super(s.toInt) //<-- error: 'this' expected but 'super' found.
    }
}

Thanks,
Zemian Deng

[Jamie Webb-2]

On 2008-02-21 13:29:19 Zemian Deng wrote:

> hello list,
>
> Is there a super() method in Scala that I can do things like this?
>
> class A(x:Int){
>     override def toString={x.toString}
> }
> class B extends A(0) {
>   def this(s:String)={
>       super(s.toInt) //<-- error: 'this' expected but 'super' found.
>     }
> }

No. Superclass parameters can only be specified in the primary
constructor. This is a limitation of Scala compared to Java, but it's
really just enforcing good practise. In your example, you could do:

  class B private (x : Int) extends A(x) {
      def this = this(0)
      def this(s : String) = this(s.toInt)
  }

/J

[Blair Zajac-3]

Zemian Deng wrote:

> hello list,
>
> Is there a super() method in Scala that I can do things like this?
>
> class A(x:Int){
>     override def toString={x.toString}
> }
> class B extends A(0) {
>   def this(s:String)={
>       super(s.toInt) //<-- error: 'this' expected but 'super' found.

No, there isn't a way.  You have to use the primary constructor.

Blair

[Steve Bendiola]

Zemian,

You can don't need the extra constructor, you can to the toInt conversion inline

class B(s:String) extends A(s.toInt) { }

Steve

On Thu, Feb 21, 2008 at 12:29 PM, Zemian Deng <[hidden email]> wrote:

hello list,

Is there a super() method in Scala that I can do things like this?

class A(x:Int){
    override def toString={x.toString}
}
class B extends A(0) {
  def this(s:String)={
      super(s.toInt) //<-- error: 'this' expected but 'super' found.
    }
}

Thanks,
Zemian Deng

[Christos KK Loverdos]

For the given example, this should do:

class B(s: String) extends A(s.toInt)

On Thu, Feb 21, 2008 at 8:29 PM, Zemian Deng <[hidden email]> wrote:

> hello list,
>
> Is there a super() method in Scala that I can do things like this?
>
> class A(x:Int){
>     override def toString={x.toString}
> }
> class B extends A(0) {
>   def this(s:String)={
>       super(s.toInt) //<-- error: 'this' expected but 'super' found.
>      }
> }
>
> Thanks,
> Zemian Deng
>

--
 __~O
 -\ <, Christos KK Loverdos
(*)/ (*) http://ckkloverdos.com

[Eric Willigers]

Zemian Deng wrote:

> hello list,
>
> Is there a super() method in Scala that I can do things like this?
>
> class A(x:Int){
>     override def toString={x.toString}
> }
> class B extends A(0) {
>   def this(s:String)={
>       super(s.toInt) //<-- error: 'this' expected but 'super' found.
>     }
> }
>
> Thanks,
> Zemian Deng

No. You'll need

class B private(n: Int) extends A(n) {
   def this(s:String)={
     this(s.toInt)
   }

   def this()={
     this(0)
   }
}

The "private" is optional - it allows you to still only expose the same
two constructors to users.

[Zemian Deng]

Hum... maybe the example I provided is not very good. So let's try again. If I have a closed source Java library that provided this:
class S1
class S2
class A -> has 3 over loaded constructors that I can do following:
new A()
new A(new S1)
new A(new S2)
And unfortunately the class A is closed source and no setter methods is exposed! S1 and S2 is not related and not convertible.

Now if I were to write a Scala class that inherit from A and want to cover all constructor cases, my first thought was I can do things with a super constructor call like ...
class B extends A{
  def this(s1:S1) super(s1)
  def this(s2:S2) super(s2)
}

But now that I know super doesn't exists, but I still can't find a way to cover all constructors. Can you provide me a sample of workaround again based on above scenerio?

Much thanks,
-zemian

On Thu, Feb 21, 2008 at 5:15 PM, Eric Willigers <[hidden email]> wrote:

Zemian Deng wrote:
> hello list,
>
> Is there a super() method in Scala that I can do things like this?
>
> class A(x:Int){
>     override def toString={x.toString}
> }
> class B extends A(0) {
>   def this(s:String)={
>       super(s.toInt) //<-- error: 'this' expected but 'super' found.
>     }
> }
>
> Thanks,
> Zemian Deng

No. You'll need

class B private(n: Int) extends A(n) {

  def this(s:String)={
    this(s.toInt)
  }

  def this()={
    this(0)
  }
}

The "private" is optional - it allows you to still only expose the same
two constructors to users.

[Erkki Lindpere-2]

It seems that you could do this:

class B extends A
class BWithS1(s1: S1) extends A(s1)
class BWithS2(s2: S2) extends A(s2)

I don't think it's possible without creating a separate type in Scala
for each constructor.

Zemian Deng wrote:

> Hum... maybe the example I provided is not very good. So let's try
> again. If I have a closed source Java library that provided this:
> class S1
> class S2
> class A -> has 3 over loaded constructors that I can do following:
> new A()
> new A(new S1)
> new A(new S2)
> And unfortunately the class A is closed source and no setter methods
> is exposed! S1 and S2 is not related and not convertible.
>
> Now if I were to write a Scala class that inherit from A and want to
> cover all constructor cases, my first thought was I can do things with
> a super constructor call like ...
> class B extends A{
>   def this(s1:S1) super(s1)
>   def this(s2:S2) super(s2)
> }
>
> But now that I know super doesn't exists, but I still can't find a way
> to cover all constructors. Can you provide me a sample of workaround
> again based on above scenerio?
>
> Much thanks,
> -zemian
>
>
> On Thu, Feb 21, 2008 at 5:15 PM, Eric Willigers <[hidden email]
> <mailto:[hidden email]>> wrote:
>
>     Zemian Deng wrote:
>     > hello list,
>     >
>     > Is there a super() method in Scala that I can do things like this?
>     >
>     > class A(x:Int){
>     >     override def toString={x.toString}
>     > }
>     > class B extends A(0) {
>     >   def this(s:String)={
>     >       super(s.toInt) //<-- error: 'this' expected but 'super' found.
>     >     }
>     > }
>     >
>     > Thanks,
>     > Zemian Deng
>
>     No. You'll need
>
>     class B private(n: Int) extends A(n) {
>       def this(s:String)={
>         this(s.toInt)
>       }
>
>       def this()={
>         this(0)
>       }
>     }
>
>     The "private" is optional - it allows you to still only expose the
>     same
>     two constructors to users.
>
>