Covariant problem

[Sivo Schilling]

Zarathustra Wrote:

> Koroskin Denis Wrote:
> 
> > On Thu, 24 Jul 2008 17:23:44 +0400, Zarathustra  
> > <adam.chrapkowski at 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);
}
---