On Thu, 24 Jul 2008 15:19:59 +0400, Zarathustra <adam.chrapkowski@gmail.com> wrote:

> Steven Schveighoffer Wrote:
>
>>
>> "Zarathustra" wrote
>> > Steven Schveighoffer Wrote:
>> >
>> >> "Zarathustra" wrote
>> >> > error:
>> >> > function basis.CPolygon2d.getPoints of type CPoint2d[]() overrides  
>> but
>> >> > is
>> >> > not covariant with basis.CPolygon3d.getPoints of type CPoint3d[]()
>> >> >
>> >> > I don't know how to fix this problem. What does 'covariant' mean?
>> >>
>> >> Covariant means that the override returns something that can be
>> >> implicitly
>> >> casted to the base version.
>> >>
>> >> So the error looks like the base class function getPoints returns  
>> type
>> >> CPoint3d[], but the derived class is returning CPoint2d[].  In order  
>> for
>> >> this to work, CPoint2d[] must be implicitly castable to CPoint3d[],  
>> which
>> >> probably isn't true.
>> >>
>> >> In order to diagnose the problem exactly, we would have to see  
>> code.  At
>> >> least the class hierarchy.
>> >>
>> >> -Steve
>> >>
>> >>
>> >
>> > Ok, thanks. I understand it now.
>> > CPoint2d class is inherited by CPoint3d. Both classes have same named
>> > functions with this difference that one return CPoint2d object and  
>> second
>> > CPoin3d object. Is possible to extort to call correct function (not  
>> from
>> > parent class). It's strange, because CPoint2d can be casted to  
>> CPoint3d
>> > but not inversely.
>>
>> I'm not quite sure how to interpret your statement.  It might be better to
>> understand by showing some stub code.
>>
>> Fill in where you see ???:
>>
>> class CPoint2d : ???
>> {
>> }
>>
>> class CPoint3d : ???
>> {
>> }
>>
>> class CPolygon2d : ???
>> {
>>   ???[] getPoints() {}
>> }
>>
>> class CPolygon3d : ???
>> {
>>   ???[] getPoints() {}
>> }
>>
>> -Steve
>>
>>
>
> class CPoint3d{
> }
>
> class CPoint2d : CPoint3d{
> }
>
> class CPolygon3d{
>   CPoint3d [] getPoints() {}
> }
> class CPolygon2d : CPolygon3d{
>   CPoint2d [] getPoints() {}
> }

Well, it *should* work based on current semantics, because CPoint2d[] implicitly castable to CPoint3d[]. Moreover, it compiles with D2 but doesn't with D1. However, it is error-prone (as I showed previously) and is therefore better to avoid. Besides, it's an arguable design to inherit CPoint2d from CPoint3d :)

Koroskin Denis Wrote:

> On Thu, 24 Jul 2008 15:19:59 +0400, Zarathustra <adam.chrapkowski@gmail.com> wrote:
> 
> > Steven Schveighoffer Wrote:
> >
> >>
> >> "Zarathustra" wrote
> >> > Steven Schveighoffer Wrote:
> >> >
> >> >> "Zarathustra" wrote
> >> >> > error:
> >> >> > function basis.CPolygon2d.getPoints of type CPoint2d[]() overrides
> >> but
> >> >> > is
> >> >> > not covariant with basis.CPolygon3d.getPoints of type CPoint3d[]()
> >> >> >
> >> >> > I don't know how to fix this problem. What does 'covariant' mean?
> >> >>
> >> >> Covariant means that the override returns something that can be
> >> >> implicitly
> >> >> casted to the base version.
> >> >>
> >> >> So the error looks like the base class function getPoints returns
> >> type
> >> >> CPoint3d[], but the derived class is returning CPoint2d[].  In order
> >> for
> >> >> this to work, CPoint2d[] must be implicitly castable to CPoint3d[],
> >> which
> >> >> probably isn't true.
> >> >>
> >> >> In order to diagnose the problem exactly, we would have to see
> >> code.  At
> >> >> least the class hierarchy.
> >> >>
> >> >> -Steve
> >> >>
> >> >>
> >> >
> >> > Ok, thanks. I understand it now.
> >> > CPoint2d class is inherited by CPoint3d. Both classes have same named
> >> > functions with this difference that one return CPoint2d object and
> >> second
> >> > CPoin3d object. Is possible to extort to call correct function (not
> >> from
> >> > parent class). It's strange, because CPoint2d can be casted to
> >> CPoint3d
> >> > but not inversely.
> >>
> >> I'm not quite sure how to interpret your statement.  It might be better
> >> to
> >> understand by showing some stub code.
> >>
> >> Fill in where you see ???:
> >>
> >> class CPoint2d : ???
> >> {
> >> }
> >>
> >> class CPoint3d : ???
> >> {
> >> }
> >>
> >> class CPolygon2d : ???
> >> {
> >>   ???[] getPoints() {}
> >> }
> >>
> >> class CPolygon3d : ???
> >> {
> >>   ???[] getPoints() {}
> >> }
> >>
> >> -Steve
> >>
> >>
> >
> > class CPoint3d{
> > }
> >
> > class CPoint2d : CPoint3d{
> > }
> >
> > class CPolygon3d{
> >   CPoint3d [] getPoints() {}
> > }
> > class CPolygon2d : CPolygon3d{
> >   CPoint2d [] getPoints() {}
> > }
> 
> Well, it *should* work based on current semantics, because CPoint2d[] implicitly castable to CPoint3d[]. Moreover, it compiles with D2 but doesn't with D1. However, it is error-prone (as I showed previously) and is therefore better to avoid. Besides, it's an arguable design to inherit CPoint2d from CPoint3d :)

Thanks, but Inheriting is ok, because point2d is also point3d but with this difference it is located on a plane.
Point2d have coordinates x, y, z in relation to the space coordinate system and coordinates x, y in relation to the plane coordinate system. But it's only thad by the way ;p
I use D1. Hmm in my opinion it should work. Ok little more code:
class CPoint3d{
  //______________________________________
  //  ::>> Attributes <<::
  //

  //______________________________________
  //  << fields >>

  private long m_x;
  private long m_y;
  private long m_z;
  //...

  //______________________________________
  //  << properties >>

  // property x
  //______________________________________
  public long x(long o_x){ return this.m_x = o_x; }
  public long x(            ){ return this.m_x          ; }

  // property y
  //______________________________________
  public long y(long o_y){ return this.m_y = o_y; }
  public long y(            ){ return this.m_y         ; }

  // property z
  //______________________________________
  public long z(long o_z){ return this.m_z = o_z; }
  public long z(            ){ return this.m_z         ; }

  //...
}
class CPoint2d : CPoint3d{
  //______________________________________
  //  ::>> Attributes <<::
  //

  //______________________________________
  //  << fields >>

  private long m_x;
  private long m_y;
  //...

  //______________________________________
  //  << properties >>

  // property x
  //______________________________________
  public long x(long o_x){ return this.m_x = o_x; }
  public long x(            ){ return this.m_x          ; }

  // property y
  //______________________________________
  public long y(long o_y){ return this.m_y = o_y; }
  public long y(            ){ return this.m_y         ; }

  //...
}

class CPolygon3d{
  //______________________________________
  //  ::>> Attributes <<::
  //

  //______________________________________
  //  << fields >>
  //...
  private CPoint3d [] m_points;
  //...

  //______________________________________
  //  << properties >>
  //...

  // property getPoints
  //______________________________________
  public CPoint3d [] getPoints(){ return this.GetPoints; }

  //...

  //______________________________________
  //  ::>> Methods <<::
  //

  //...

  //______________________________________
  //  << operations >>

  //...
  private CPoint3d []
  GetPoints()
  in{
    //...
  }
  out{
    //...
  }
  body{
    //...
  }
}

class CPolygon2d : CPolygon3d{
  //______________________________________
  //  ::>> Attributes <<::
  //

  //______________________________________
  //  << fields >>
  //...
  private CPoint2d [] m_points;
  //...

  //______________________________________
  //  << properties >>
  //...

  // property getPoints
  //______________________________________
  public CPoint2d [] getPoints(){ return this.GetPoints; } // <- error is here

  //...

  //______________________________________
  //  ::>> Methods <<::
  //

  //...

  //______________________________________
  //  << operations >>

  //...
  private CPoint2d []
  GetPoints()
  in{
    //...
  }
  out{
    //...
  }
  body{
    //...
  }
}

For me it's unreasonable because CPoint3d can not be casted to CPoint2d :( Ech ;/

Ok, more code :P beacuse problem is only with arrays.
class CPolygon3d{
  //______________________________________
  //  ::>> Attributes <<::
  //

  //______________________________________
  //  << fields >>
  //...
  private CPoint3d [] m_points;
  //...

  //______________________________________
  //  << properties >>
  //...

  // property getPoint
  //______________________________________
  public CPoint3d getPoint(){ return this.GetPoint; }

  // property getPoints
  //______________________________________
  public CPoint3d [] getPoints(){ return this.GetPoints; }

  //...

  //______________________________________
  //  ::>> Methods <<::
  //

  //...

  //______________________________________
  //  << operations >>

  //...

  // operation GetPoint
  //______________________________________
  private CPoint3d
  GetPoint()
  in{
    //...
  }
  out{
    //...
  }
  body{
    //...
  }

  // operation GetPoints
  //______________________________________
  private CPoint3d []
  GetPoints()
  in{
    //...
  }
  out{
    //...
  }
  body{
    //...
  }
}

class CPolygon2d : CPolygon3d{
  //______________________________________
  //  ::>> Attributes <<::
  //

  //______________________________________
  //  << fields >>
  //...
  private CPoint2d [] m_points;
  //...

  //______________________________________
  //  << properties >>
  //...

  // property getPoint
  //______________________________________
  public CPoint2d getPoint(){ return this.GetPoint; }  // ok

  // property getPoints
  //______________________________________
  public CPoint2d [] getPoints(){ return this.GetPoints; } // problem

  //...

  //______________________________________
  //  ::>> Methods <<::
  //

  //...

  //______________________________________
  //  << operations >>

  //...

  // opeartion GetPoint
  //______________________________________
  private CPoint2d
  GetPoint()
  in{
    //...
  }
  out{
    //...
  }
  body{
    //...
  }

  // opeartion GetPoints
  //______________________________________
  private CPoint2d []
  GetPoints()
  in{
    //...
  }
  out{
    //...
  }
  body{
    //...
  }

}

Sorry, for the amount of posts, but below is full and most easy example program which ilustrates problem ;)
________________________________________________________
// class CFoo
//_______________________________________________
class CFoo{
  //_____________________________________________
  //  ::>> Attributes <<::
  //

  //_____________________________________________
  //  << fields >>

  public real [] test(){ return [3.4, 4.5]; }
}

// class CBar
//_________________________________________________
class CBar : CFoo{
    //_____________________________________________
  //  ::>> Attributes <<::
  //

  //_____________________________________________
  //  << fields >>
  public uint [] test(){ return [9, 8, 7]; }
}

void
main(char [][] args){
}
________________________________________________________

On Thu, 24 Jul 2008 17:23:44 +0400, Zarathustra <adam.chrapkowski@gmail.com> wrote:

> Sorry, for the amount of posts, but below is full and most easy example program which ilustrates problem ;)
> ________________________________________________________
> // class CFoo
> //_______________________________________________
> class CFoo{
>   //_____________________________________________
>   //  ::>> Attributes <<::
>   //
>
>   //_____________________________________________
>   //  << fields >>
>  public real [] test(){ return [3.4, 4.5]; }
> }
>
> // class CBar
> //_________________________________________________
> class CBar : CFoo{
>     //_____________________________________________
>   //  ::>> Attributes <<::
>   //
>
>   //_____________________________________________
>   //  << fields >>
>   public uint [] test(){ return [9, 8, 7]; }
> }
>
> void
> main(char [][] args){
> }
> ________________________________________________________
>


I'm sorry, but your example is incorrect. You can't cast uint[] to real[]. If you need that, write a function for the task. Compiler won't do this automatically. And yes, they are not covariant! :)

"Zarathustra" wrote
> Steven Schveighoffer Wrote:
>
>>
>> "Zarathustra" wrote
>> > Steven Schveighoffer Wrote:
>> >
>> >> "Zarathustra" wrote
>> >> > error:
>> >> > function basis.CPolygon2d.getPoints of type CPoint2d[]() overrides
>> >> > but
>> >> > is
>> >> > not covariant with basis.CPolygon3d.getPoints of type CPoint3d[]()
>> >> >
>> >> > I don't know how to fix this problem. What does 'covariant' mean?
>> >>
>> >> Covariant means that the override returns something that can be
>> >> implicitly
>> >> casted to the base version.
>> >>
>> >> So the error looks like the base class function getPoints returns type
>> >> CPoint3d[], but the derived class is returning CPoint2d[].  In order
>> >> for
>> >> this to work, CPoint2d[] must be implicitly castable to CPoint3d[],
>> >> which
>> >> probably isn't true.
>> >>
>> >> In order to diagnose the problem exactly, we would have to see code.
>> >> At
>> >> least the class hierarchy.
>> >>
>> >> -Steve
>> >>
>> >>
>> >
>> > Ok, thanks. I understand it now.
>> > CPoint2d class is inherited by CPoint3d. Both classes have same named
>> > functions with this difference that one return CPoint2d object and
>> > second
>> > CPoin3d object. Is possible to extort to call correct function (not
>> > from
>> > parent class). It's strange, because CPoint2d can be casted to CPoint3d
>> > but not inversely.
>>
>> I'm not quite sure how to interpret your statement.  It might be better
>> to
>> understand by showing some stub code.
>>
>> Fill in where you see ???:
>>
>> class CPoint2d : ???
>> {
>> }
>>
>> class CPoint3d : ???
>> {
>> }
>>
>> class CPolygon2d : ???
>> {
>>   ???[] getPoints() {}
>> }
>>
>> class CPolygon3d : ???
>> {
>>   ???[] getPoints() {}
>> }
>>
>> -Steve
>>
>>
>
> class CPoint3d{
> }
>
> class CPoint2d : CPoint3d{
> }
>
> class CPolygon3d{
>  CPoint3d [] getPoints() {}
> }
> class CPolygon2d : CPolygon3d{
>  CPoint2d [] getPoints() {}
> }

If this does not work, then I would say it is a bug.  You should file it with this example code, fill in the function bodies, and paste the errors that result from it.

-Steve

Koroskin Denis Wrote:

> On Thu, 24 Jul 2008 17:23:44 +0400, Zarathustra <adam.chrapkowski@gmail.com> wrote:
> 
> > Sorry, for the amount of posts, but below is full and most easy example
> > program which ilustrates problem ;)
> > ________________________________________________________
> > // class CFoo
> > //_______________________________________________
> > class CFoo{
> >   //_____________________________________________
> >   //  ::>> Attributes <<::
> >   //
> >
> >   //_____________________________________________
> >   //  << fields >>
> >  public real [] test(){ return [3.4, 4.5]; }
> > }
> >
> > // class CBar
> > //_________________________________________________
> > class CBar : CFoo{
> >     //_____________________________________________
> >   //  ::>> Attributes <<::
> >   //
> >
> >   //_____________________________________________
> >   //  << fields >>
> >   public uint [] test(){ return [9, 8, 7]; }
> > }
> >
> > void
> > main(char [][] args){
> > }
> > ________________________________________________________
> >
> 
> 
> I'm sorry, but your example is incorrect. You can't cast uint[] to real[]. If you need that, write a function for the task. Compiler won't do this automatically. And yes, they are not covariant! :)

Of course ;) You have a right ;p
I'm blind. Now I see that I tied do something like that:
typeA function(typeX x){}
typeB function(typeX x){}
of cource compiler which function call ;p sorry my very very stiupid mistake.

Zarathustra Wrote:

> Koroskin Denis Wrote:
> 
> > On Thu, 24 Jul 2008 17:23:44 +0400, Zarathustra <adam.chrapkowski@gmail.com> wrote:
> > 
> > > Sorry, for the amount of posts, but below is full and most easy example
> > > program which ilustrates problem ;)
> > > ________________________________________________________
> > > // class CFoo
> > > //_______________________________________________
> > > class CFoo{
> > >   //_____________________________________________
> > >   //  ::>> Attributes <<::
> > >   //
> > >
> > >   //_____________________________________________
> > >   //  << fields >>
> > >  public real [] test(){ return [3.4, 4.5]; }
> > > }
> > >
> > > // class CBar
> > > //_________________________________________________
> > > class CBar : CFoo{
> > >     //_____________________________________________
> > >   //  ::>> Attributes <<::
> > >   //
> > >
> > >   //_____________________________________________
> > >   //  << fields >>
> > >   public uint [] test(){ return [9, 8, 7]; }
> > > }
> > >
> > > void
> > > main(char [][] args){
> > > }
> > > ________________________________________________________
> > >
> > 
> > 
> > I'm sorry, but your example is incorrect. You can't cast uint[] to real[]. If you need that, write a function for the task. Compiler won't do this automatically. And yes, they are not covariant! :)
> 
> Of course ;) You have a right ;p
> I'm blind. Now I see that I tied do something like that:
> typeA function(typeX x){}
> typeB function(typeX x){}
> of cource compiler which function call ;p sorry my very very stiupid mistake.

If you consider functions, e.g. not class members you're right, but this
is not your point. You can achive your task if you make the test() member
in CFoo final. That means CFoo.test is no longer virtual and therefore it is not necessary to have a covariant return type for CBar.test.
Your example above with the main function containing a simple test
scenario compiles and runs with both DMD 1.033 and DMD 2.017 quite well:

---
import std.stdio;

// class CFoo
//_______________________________________________
class CFoo{
  //_____________________________________________
  //  ::>> Attributes <<::
  //

  //_____________________________________________
  //  << fields >>
  // public real [] test(){ return [3.4, 4.5]; }
  final public real [] test(){ return [3.4, 4.5]; }
}

// class CBar
//_________________________________________________
class CBar : CFoo{
    //_____________________________________________
  //  ::>> Attributes <<::
  //

  //_____________________________________________
  //  << fields >>
  public uint [] test(){ return [9, 8, 7]; }
}

void
main(char [][] args){
    CFoo foo = new CFoo;
    CBar bar = new CBar;

    writefln("foo.test() gives %s as expected.", foo.test);
    writefln("bar.test() gives %s as expected.", bar.test);
}
---

Sivo Schilling Wrote:

> Zarathustra Wrote:
> 
> > Koroskin Denis Wrote:
> > 
> > > On Thu, 24 Jul 2008 17:23:44 +0400, Zarathustra <adam.chrapkowski@gmail.com> wrote:
> > > 
> > > > Sorry, for the amount of posts, but below is full and most easy example
> > > > program which ilustrates problem ;)
> > > > ________________________________________________________
> > > > // class CFoo
> > > > //_______________________________________________
> > > > class CFoo{
> > > >   //_____________________________________________
> > > >   //  ::>> Attributes <<::
> > > >   //
> > > >
> > > >   //_____________________________________________
> > > >   //  << fields >>
> > > >  public real [] test(){ return [3.4, 4.5]; }
> > > > }
> > > >
> > > > // class CBar
> > > > //_________________________________________________
> > > > class CBar : CFoo{
> > > >     //_____________________________________________
> > > >   //  ::>> Attributes <<::
> > > >   //
> > > >
> > > >   //_____________________________________________
> > > >   //  << fields >>
> > > >   public uint [] test(){ return [9, 8, 7]; }
> > > > }
> > > >
> > > > void
> > > > main(char [][] args){
> > > > }
> > > > ________________________________________________________
> > > >
> > > 
> > > 
> > > I'm sorry, but your example is incorrect. You can't cast uint[] to real[]. If you need that, write a function for the task. Compiler won't do this automatically. And yes, they are not covariant! :)
> > 
> > Of course ;) You have a right ;p
> > I'm blind. Now I see that I tied do something like that:
> > typeA function(typeX x){}
> > typeB function(typeX x){}
> > of cource compiler which function call ;p sorry my very very stiupid mistake.
> 
> If you consider functions, e.g. not class members you're right, but this
> is not your point. You can achive your task if you make the test() member
> in CFoo final. That means CFoo.test is no longer virtual and therefore it is not necessary to have a covariant return type for CBar.test.
> Your example above with the main function containing a simple test
> scenario compiles and runs with both DMD 1.033 and DMD 2.017 quite well:
> 
> ---
> import std.stdio;
> 
> // class CFoo
> //_______________________________________________
> class CFoo{
>   //_____________________________________________
>   //  ::>> Attributes <<::
>   //
> 
>   //_____________________________________________
>   //  << fields >>
>   // public real [] test(){ return [3.4, 4.5]; }
>   final public real [] test(){ return [3.4, 4.5]; }
> }
> 
> // class CBar
> //_________________________________________________
> class CBar : CFoo{
>     //_____________________________________________
>   //  ::>> Attributes <<::
>   //
> 
>   //_____________________________________________
>   //  << fields >>
>   public uint [] test(){ return [9, 8, 7]; }
> }
> 
> void
> main(char [][] args){
>     CFoo foo = new CFoo;
>     CBar bar = new CBar;
> 
>     writefln("foo.test() gives %s as expected.", foo.test);
>     writefln("bar.test() gives %s as expected.", bar.test);
> }
> ---
> 

Great, thanks!
It's exactly that what I need.
all regards