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C# C# Objects Inheritance Inheritance in Code

Posted by Jack Stone
Jack Stone
9,838 Points

C# Inheritance: console coming back with difference to tutorial

Hello,

I've ran my code and can't see where what I've written deviates from the video so I need a second pair of eyes to assist.

Game.cs(13,17): warning CS0219: The variable `p' is assigned but its value is never used
Compilation succeeded - 1 warning(s)
3
False
True
False

As the console shows two 'false's and one 'true' when the top 'false' should be a true.

my code is as follows:

(Game.cs)

using System;

namespace TreehouseDefence
{
    class Game
    {
        public static void Main()
        {
            Map map = new Map(8, 5);

          Point x = new Point (4, 2);  

          Point p = x;

          map.OnMap (new MapLocation(0,0));

         Console.WriteLine(x.DistanceTo (5, 5));

          Console.WriteLine(x is MapLocation);
          Console.WriteLine(x is Point);

          Point point = new Point (0,0);
          Console.WriteLine(point is MapLocation);
        }
    }
}

(MapLocation.cs)

namespace TreehouseDefence
{
    class MapLocation : Point
    {

        public MapLocation (int x, int y) : base(x, y)
      {

      }

    }

}

1 Answer

andren
andren
28,558 Points
andren
andren
28,558 Points

The issue is this line:

Point x = new Point (4, 2);

The first test produces false because x is not a MapLocation, it is a Point since that is what you assigned to it.

The line should be:

Point x = new MapLocation (4, 2);

The above line might look wrong since you define x as holding a Point object, not a MapLocation object. But it is valid code because MapLocation is a type of Point, due to how it's inheritance is setup. Which means that you can in fact treat it as a Point object.