the code at the end of posting compiles but when run causes Error: Access Violation

however ... if callLayout was defined as
void callLayout( CanLayout cl ) {
    cl.doLayout();
}
it works (the compiler knows BaseLayout implements CanLayout [in main])
as does
void callLayoutInd(CanLayout cl) {
 if ( cl ) {
  cl.doLayout();
 } else {
  println( "the 'Base' you passed did not implement 'CanLayout'" );
 }
}
void callLayout( Base b ) {
 callLayoutInd( cast(BaseLayout)b );
}

is this intended "interface" behaviour ? [have I missed a big point with D interfaces?] (would wish for a more "Java" interface).

------------------
//
// interface test 001
//
import c.stdio;

void println( char[] str ) { printf( "%.*s\n", str ); }

interface CanLayout {
 void doLayout();
}

class Base {
 void print() { println("Base::print"); }
}

class BaseLayout : Base, CanLayout {
 void doLayout() { println( "BaseLayout::doLayout" ); }
}

void callLayout( Base b ) {
 CanLayout cl = cast(CanLayout)b;
 if ( cl ) {
  cl.doLayout();
 } else {
  println( "the 'Base' you passed did not implement 'CanLayout'" );
 }
}

int main( char[][] args ) {
 callLayout( new BaseLayout() );
 return 0;
}

Yes, it's intended to work that way, although I'll investigate why there's a crash rather than just getting a null pointer.

"Mike Wynn" <mike.wynn@l8night.co.uk> wrote in message news:bhil4u$2hj6$1@digitaldaemon.com...
> the code at the end of posting compiles but when run causes Error: Access Violation
>
> however ... if callLayout was defined as
> void callLayout( CanLayout cl ) {
>     cl.doLayout();
> }
> it works (the compiler knows BaseLayout implements CanLayout [in main])
> as does
> void callLayoutInd(CanLayout cl) {
>  if ( cl ) {
>   cl.doLayout();
>  } else {
>   println( "the 'Base' you passed did not implement 'CanLayout'" );
>  }
> }
> void callLayout( Base b ) {
>  callLayoutInd( cast(BaseLayout)b );
> }
>
> is this intended "interface" behaviour ? [have I missed a big point with D interfaces?] (would wish for a more "Java" interface).
>
> ------------------
> //
> // interface test 001
> //
> import c.stdio;
>
> void println( char[] str ) { printf( "%.*s\n", str ); }
>
> interface CanLayout {
>  void doLayout();
> }
>
> class Base {
>  void print() { println("Base::print"); }
> }
>
> class BaseLayout : Base, CanLayout {
>  void doLayout() { println( "BaseLayout::doLayout" ); }
> }
>
> void callLayout( Base b ) {
>  CanLayout cl = cast(CanLayout)b;
>  if ( cl ) {
>   cl.doLayout();
>  } else {
>   println( "the 'Base' you passed did not implement 'CanLayout'" );
>  }
> }
>
> int main( char[][] args ) {
>  callLayout( new BaseLayout() );
>  return 0;
> }
>
>

"Walter" <walter@digitalmars.com> wrote in message news:bhj2rf$2tm2$1@digitaldaemon.com...
> Yes, it's intended to work that way, although I'll investigate why there's
a
> crash rather than just getting a null pointer.

why can't I cast an instance of BaseLayout (passed as Base) to an interface
it implements ?
this behaviour makes D even more restricive to use than Java, and seems to
contradict the whole idea of interfaces (a set of methods any Object can
implement) allowing limited MI like behavious.

> "Mike Wynn" <mike.wynn@l8night.co.uk> wrote in message news:bhil4u$2hj6$1@digitaldaemon.com...
> > the code at the end of posting compiles but when run causes Error: Access Violation
> >
> > however ... if callLayout was defined as
> > void callLayout( CanLayout cl ) {
> >     cl.doLayout();
> > }
> > it works (the compiler knows BaseLayout implements CanLayout [in main])
> > as does
> > void callLayoutInd(CanLayout cl) {
> >  if ( cl ) {
> >   cl.doLayout();
> >  } else {
> >   println( "the 'Base' you passed did not implement 'CanLayout'" );
> >  }
> > }
> > void callLayout( Base b ) {
> >  callLayoutInd( cast(BaseLayout)b );
> > }
> >
> > is this intended "interface" behaviour ? [have I missed a big point with
D
> > interfaces?] (would wish for a more "Java" interface).
> >
> > ------------------
> > //
> > // interface test 001
> > //
> > import c.stdio;
> >
> > void println( char[] str ) { printf( "%.*s\n", str ); }
> >
> > interface CanLayout {
> >  void doLayout();
> > }
> >
> > class Base {
> >  void print() { println("Base::print"); }
> > }
> >
> > class BaseLayout : Base, CanLayout {
> >  void doLayout() { println( "BaseLayout::doLayout" ); }
> > }
> >
> > void callLayout( Base b ) {
> >  CanLayout cl = cast(CanLayout)b;
> >  if ( cl ) {
> >   cl.doLayout();
> >  } else {
> >   println( "the 'Base' you passed did not implement 'CanLayout'" );
> >  }
> > }
> >
> > int main( char[][] args ) {
> >  callLayout( new BaseLayout() );
> >  return 0;
> > }
> >
> >
>
>