collections/collection/naive/simple.cs - A collection of up to three instance variables of type T - with an iterator.

Lecture 12 - slide 35 : 36 Program 1

using System;
using System.Collections.Generic;
using System.Collections;

public class GivenCollection<T> : IEnumerable<T>{
 
  private T first, second, third;
  private bool firstDefined, secondDefined, thirdDefined;
 
  public GivenCollection(){
    this.firstDefined = false; 
    this.secondDefined = false;
    this.thirdDefined = false; 
  }

  public GivenCollection(T first){
    this.first = first; 
    this.firstDefined = true;
    this.secondDefined = false;
    this.thirdDefined = false; 
  }

  public GivenCollection(T first, T second){
    this.first = first;
    this.second = second; 
    this.firstDefined = true;
    this.secondDefined = true;
    this.thirdDefined = false; 
  }

  public GivenCollection(T first, T second, T third){
    this.first = first;
    this.second = second;
    this.third = third;
    this.firstDefined = true;
    this.secondDefined = true;
    this.thirdDefined = true; 
  }

  public int Count(){
    int res;
    if (!firstDefined) res = 0;
    else if (!secondDefined) res = 1;
    else if (!thirdDefined) res = 2;
    else res = 3;
    return res;
  }

  public IEnumerator<T> GetEnumerator(){
    if (firstDefined) yield return first;
    if (secondDefined) yield return second;  // not else
    if (thirdDefined) yield return third;    // not else
  }

  IEnumerator IEnumerable.GetEnumerator(){
    return GetEnumerator();
  }

}