C# Online Compiler | .NET Fiddle

using System;
using System.Collections;
using System.Collections.Generic;
					
public class Program
{
	public static void Main()
	{
		Console.WriteLine("Hello World");
		
		#region Contravarient Usage Types
			
		//Type 1 - Passing objects
			Toyota MyCar = new Toyota();
			Honda MyWifeCar  = new Honda();
			Console.WriteLine("============================");
			ShowColor(MyCar); //Contravarient 
			ShowColor(MyWifeCar); //Contravarient 
		
		//Type 2 -  Passing List<Objects>
			List<Car> mycars = new List<Car>();
			mycars.Add(MyCar);
			mycars.Add(MyWifeCar);
			Console.WriteLine("============================");
			ShowColor(mycars);
		
		//Type 3 - Passing IEnumerable<Objects>
			IEnumerable<Car> myIEnumCars = mycars;
			Console.WriteLine("============================");
			ShowColor(myIEnumCars);
		
		//Type4 - Passing Delegates
			ContraVarientDelegateType<Car> mydel = ShowColor; // Using Named Method
			ContraVarientDelegateType<Car> mydel1 = (car) =>  car.DisplayColor(); // Using Unanymous Or Lamda Expression
		Console.WriteLine("============================");
			mydel(MyCar);
			mydel1(MyWifeCar);
        #endregion 
			 
	}
	
	#region Contravarient Methods
		
	delegate void ContraVarientDelegateType <in T> (T a);
	
	private static void ShowColor(Car car)
	{
		car.DisplayColor();
	}
	private static void ShowColor(List<Car> cars)
	{
		Console.WriteLine("List of Car colors ==>: ");
		foreach(Car displaycar in cars)
			displaycar.DisplayColor();
	}
	
		private static void ShowColor(IEnumerable<Car> cars)
	{
		Console.WriteLine("List of IEnum Car colors ==>: ");
		foreach(Car displaycar in cars)
			displaycar.DisplayColor();
	}
	#endregion 
		
}


public class Car
{
	private string color = "red";
	
	public virtual void DisplayColor()
	{
		Console.WriteLine(" color : " + color );
	}
}

public class Toyota : Car
{ 
	private string color = "Totota red";
	
	public override void DisplayColor()
	{
		Console.WriteLine(" color : " + color );
	}
}

public class Honda : Car
{
	private string color = "Honda red";
	
	public override void DisplayColor()
	{
		Console.WriteLine("color : " + color );
	}
	
}

 
using System;
using System.Collections;
using System.Collections.Generic;
                    
public class Program
{
    public static void Main()
    {
        Console.WriteLine("Hello World");
        
        #region Contravarient Usage Types
            
        //Type 1 - Passing objects
            Toyota MyCar = new Toyota();
            Honda MyWifeCar  = new Honda();
            Console.WriteLine("============================");
            ShowColor(MyCar); //Contravarient 
            ShowColor(MyWifeCar); //Contravarient 
        
        //Type 2 -  Passing List<Objects>
            List<Car> mycars = new List<Car>();
            mycars.Add(MyCar);
            mycars.Add(MyWifeCar);
            Console.WriteLine("============================");

Cached Result

Distinct() on both values
(1, 12)
(1, 2)
(1, 18)
(2, 12)
GroupBy() second value
(1, 12)
(1, 2)
(1, 18)