Composite

Compose objects into tree structures to represent part-whole hierarchies, letting clients treat individual objects and compositions of objects uniformly. Use it when you want to represent part-whole hierarchies and when you want clients to be able to ignore the difference between compositions of objects and individual objects.

Examples:

• An army consists of divisions, each containing brigades, which contain platoons, which contain squads of individual soldiers. An order ('march!') is issued at the top and passed down each level — the same command works on a single soldier (leaf) or an entire army (composite) through a shared execute() interface.

// Component interface shared by Leaf and Composite
class Graphic {
public:
  virtual void Draw(const Point& at) = 0;
  virtual void Add(Graphic*) {}
  virtual void Remove(Graphic*) {}
  virtual List<Graphic*>::Iterator* CreateIterator() { return 0; }
};

class Picture : public Graphic {
public:
  void Draw(const Point& at) override;
  void Add(Graphic* g) override { _graphics.Append(g); }
private:
  List<Graphic*> _graphics;
};

Synonyms: object tree