/ Design Patterns / Structural patterns / Composite

Composite Design Pattern in C++

Composite design pattern - multiple container classes

#include <iostream>
#include <vector>
using namespace std;

class Component
{
  public:
    virtual void traverse() = 0;
};

class Primitive: public Component
{
    int value;
  public:
    Primitive(int val)
    {
        value = val;
    }
    void traverse()
    {
        cout << value << "  ";
    }
};

class Composite: public Component
{
    vector < Component * > children;
    int value;
  public:
    Composite(int val)
    {
        value = val;
    }
    void add(Component *c)
    {
        children.push_back(c);
    }
    void traverse()
    {
        cout << value << "  ";
        for (int i = 0; i < children.size(); i++)
          children[i]->traverse();
    }
};

class Row: public Composite
{
  public:
    // Two different kinds of "con-
    Row(int val): Composite(val){}
    // tainer" classes.  Most of the
    void traverse()
    {
        // "meat" is in the Composite
        cout << "Row"; // base class.
        Composite::traverse();
    }
};

class Column: public Composite
{
  public:
    Column(int val): Composite(val){}
    void traverse()
    {
        cout << "Col";
        Composite::traverse();
    }
};

int main()
{
  Row first(1);                 // Row1
  Column second(2);             //   |
  Column third(3);              //   +-- Col2
  Row fourth(4);                //   |     |
  Row fifth(5);                 //   |     +-- 7
  first.add(&second);           //   +-- Col3
  first.add(&third);            //   |     |
  third.add(&fourth);           //   |     +-- Row4
  third.add(&fifth);            //   |     |     |
  first.add(&Primitive(6));     //   |     |     +-- 9
  second.add(&Primitive(7));    //   |     +-- Row5
  third.add(&Primitive(8));     //   |     |     |
  fourth.add(&Primitive(9));    //   |     |     +-- 10
  fifth.add(&Primitive(10));    //   |     +-- 8
  first.traverse();             //   +-- 6
  cout << '\n';                 
}

Output

Row1  Col2  7  Col3  Row4  9  Row5  10  8  6

Code examples

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Python Composite in Python