Talk:Trait

class ll_item;
 
class llist {
  public:
    void add(ll_item& p);
    void remove(ll_item& p);
 
    llist(void);
   ~llist();
};
 
class ll_item {
    friend llist;
  private:
    ll_item* next;
    ll_item* prev;
};
 
 
class person_item : public ll_item {
  protected:
    int age;
    const char* name;
 
  public:
    person_item(int age, const char* name);
};
 
class animal_item : public ll_item {
  protected:
    const char* name;
 
  public:
    animal_item(const char* name);
};
 
int main(int argc, char* argv[])
{
  person_item a(10, "Ben");
  person_item b(20, "Nora");
  person_item c(30, "John");
 
  animal_item x("Fifi");
  animal_item y("Bobika");
  animal_item z("Bill");
 
  llist l;
  l.add(b);
  l.add(c);
  l.add(a);
  l.add(x);
  l.add(y);
  l.add(z);
}

class persons_list : public llist {
  public:
    person_item *get(int idx)
    {
      return dynamic_cast<person_item *>(llist::get(idx));
    }
};

template<class ITEM>
class llist {
  protected:
        ITEM *first;
  public:
	void add(ITEM& p)
        {
          p.prev=NULL;
          p.next=first;
          first=&p;
        }
	void remove(ITEM& p)
        {
          ITEM *pr=p.prev;
          ITEM *nx=p.next;
          if(pr) pr->next=nx;
          else first=nx;
          if(nx) nx->prev=pr;
        }
 
        ITEM *get(int idx)
        {
          ITEM *i=first;
          while((i)&&(idx-->0))
            i=i->next;
 
          return i;
        }
 
        llist(void) { first=NULL; };
        ~llist() { };
};
 
// not inherited, requires to define next and prev properties
class person_item  {
  protected:
  int age;
  const char* name;
 
  public:
  person_item* next;
  person_item* prev;
 
  person_item (int age, const char* name) { this->age=age; this->name=name; }
};
 
 
template<class ITEM>
class ll_item  {
  friend llist <ITEM>;
private:
  ITEM* next;
  ITEM* prev;
};
 
// inherited from ll_item template which defines next and prev for me
class animal_item : public ll_item <animal_item>{
  protected:
  const char* name;
 
  public:
 
  animal_item(const char* name) : ll_item <animal_item>() { this->name=name; }
};
 
int main(int argc, char* argv[])
{
  person_item a(10, "Ben");
  person_item b(20, "Nora");
  person_item c(30, "John");
 
  animal_item x("Fifi");
  animal_item y("Bobika");
  animal_item z("Bill");
 
  llist <person_item> persons;
  persons.add(b);
  persons.add(c);
  persons.add(a);
//  persons.add(x); - compilation fails
 
  llist <animal_item> animals;
  animals.add(x);
  animals.add(y);
  animals.add(z);
}

class person_item  {
  private:
    friend llist <person_item>;
    person_item* next;
    person_item* prev;
 
  protected:
    int age;
    const char* name;
 
  public:
    person_item (int age, const char* name) { this->age=age; this->name=name; }
};