• Manfred Nowak (4/18) Oct 14 2013 -manfred
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (26/43) Oct 14 2013 That it not exactly the same but looks like the visitor pattern. The
• Manfred Nowak (13/16) Oct 14 2013 This would require changes in the whole class hierarchy.

Manfred Nowak <svv1999 hotmail.com> writes:

 class C{}
   class C1:C{}
   // ...
   class Cn:C{}
 
 C getC(){ return new Cn;} // might be extern
                           // and deliver some Ci
 
 void visit( C1 fp){}  
 // ...
 void visit( Cn fp){}  
 void main(){
   visit( getC);           // dispatch?
 }

-manfred
        
          visit( getC);
        }

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 10/14/2013 02:09 PM, Manfred Nowak wrote:

 class C{}
    class C1:C{}
    // ...
    class Cn:C{}

 C getC(){ return new Cn;} // might be extern
                            // and deliver some Ci

 void visit( C1 fp){}
 // ...
 void visit( Cn fp){}
 void main(){
    visit( getC);           // dispatch?
 }

 -manfred

            visit( getC);
          }

That it not exactly the same but looks like the visitor pattern. The 
actual type of the object is implicitly stored in the vtbl of each type. 
So, a virtual function like accept() can do the trick:

import std.stdio;

class C{
     abstract void accept();
}

class C1:C {
     override void accept() { visit(this); }
}

class Cn:C{
     override void accept() { visit(this); }
}

C getC(){ return new Cn;} // might be extern
                           // and deliver some Ci

void visit( C1 fp) {
     writeln("visiting C1");
}

void visit( Cn fp){
     writeln("visiting Cn");
}
void main(){
     getC().accept();
}

Ali

Manfred Nowak <svv1999 hotmail.com> writes:

=?UTF-8?B?QWxpIMOHZWhyZWxp?= wrote:

 a virtual function like accept() can do the trick

This would require changes in the whole class hierarchy.

But because of
 The actual type of the object is implicitly stored in the
 vtbl of each type.

and in addition, because the statement
| writeln( getC.classinfo.create.classinfo);
gives the correct type there should be a possibility to dispatch to the 
correct `visit' function without any changes in the class hierarchy.

I see that a sequence of statements
| if( auto tmp= cast(Ci) getC) visit( tmp);
can dispatch to the correct `visit' function. But this again would 
require knowledge of all `Ci'.

A solution seems very close, but ...

-manfred