Re: foreach filter by cast

[karl via Digitalmars-d-learn]

I found a solution I like a lot, with templated opApply:

class Cont{
        Thing[] kids;

        int opApply(T)(int delegate(ref T) dg){
                int result = 0;         
                for (int i = 0; i < kids.length; i++){
                        T t = cast(T)kids[i];
                        if(t){ result = dg(t);
                                if (result) break;
                        }
                }
                return result;
        }
}

class Thing{
        string name;
        this(){ name = "thing";}
}
class TBan : Thing{
        this(){ name = "tban";}
}
class TOne : Thing{
        this(){ name = "tone";}
}

void main(){
        Cont c = new Cont;
        c.kids ~= new TBan;
        c.kids ~= new TOne;
        c.kids ~= new TOne;
        c.kids ~= new Thing;

        foreach(TOne k; c){ // the "TOne k" declares the filtering-type
                writeln(k);
        }
}