Question

I have a class MySet

 class MySet
 {
   .......     
 }

This class will declare a reference to another type

(i.e)

class MySubSet
{
  ....
}

The purpose of the type MySubset is to supply “subset id” and a collection of integers to
the type MySet.

Which one of the followings is the correct implementation

(1)

  class MySet
    {
        int mySetID;
        MySubSet subset = new MySubSet();
        public int MySetID
        {
            get { return mySetID; }
            set { mySetID = value; }
        }
        public MySubSet MySubSet
        {
            get { return subset; }
            set { subset = value; }
        }
    }


   class MySubSet
    {
        int subsetID;
        List<int> subset = new List<int>();

        public List<int> SubSet
        {
            get { return subset; }
            set { subset = value; }
        }

        public int SubSetID
        {
            get { return subsetID; }
            set { subsetID = value; }
        }
    }

(2)

   class MySet
   {
      int mySetID;
       AnotherSubSet subset = new AnotherSubSet();
       public int MySetID
       {
          get { return mySetID; }
          set { mySetID = value; }
       }

       public AnotherSubSet MySubSet
       {
          get { return subset; }
          set { subset = value; }
       }
}




class AnotherSubSet : List<int>
    {
        int subsetID;
        List<int> lst = new List<int>();

        public int SubSetID
        {
            get { return subsetID; }
            set { subsetID = value; }
        }
    }

If both are worst design consideration help me to implement the one that I could follow.

Answer 1

Number 2 is better, use inheritence not composition for this pattern, – because fundementally, it is a collection. It does not contain a collection. Inheritance gives you all the functionality of the base class without the need to write pass-through functions. If you want to add a new item to the collection, using composition, you either have to add a pass through method for the Add() method to class MySubSet:

class MySubSet    
{        
    int subsetID;        
    List<int> subset = new List<int>();        
    public List<int> SubSet 
    {            
        get { return subset; }             
        set { subset = value; }        
    }        
    public void Add(int i) { subset.Add(i); }  // pass through to subset.Add()
 }

or you have to use the following non-intuitive and confusing syntax…

MySet.MySubSet.SubSet.Add(67);

with inheritence, all you need is

MySet.MySubSet.Add(67);