Equals method returns incorrect value for Geometry

Question

When comparing two Geometries of the same type (eg MapPoint) with the base class Geometry, the Equals method returns incorrect value.
Example:
MapPoint p = new MapPoint(12345,67890);
Geometry p1 = Geometry.Clone(p);
p.Equals(p1);    //Returns false
(p as MapPoint).Equals(p1 as MapPoint);    //Returns true

Both of these should return true. After all "objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program" - Liskov substitution principle.

ShawnKendrot · Answer

.Net offers the ability to override the Equals(obj) method for a reason. And that is so that you do not have to be explicit with types. The Silverlight team did a great job by allowing a user to compare to different geometries, but the work was not complete. As is mentioned in the article that Dave points  to, if you implement IEquatable, you also need to override the base Equals method. This is also the best way to implement equality checking. If for whatever reason you do not want to override Equals, then the base class (Geometry) should implement the same interface so you can compare two geometries. This method would be abstract.

JenniferNery · Answer

I understand your dilemma however, this is by design. In .NET, you have to be explicit with which Equals() you are invoking. If you cast the geometry to MapPoint, equality is checked against the points and SpatialReference, otherwise equality is checked against reference.

ShawnKendrot · Answer

The problem is that the specific Geometries use the IEquatable Equals but Geometry does not. In order to find a matching Geometry, I should not have to do the following:                
Graphic graphicToRemove = Layer.Graphics.FirstOrDefault(g =>
                        (g.Geometry != null) && (g.Geometry.GetType() == graphic.Geometry.GetType()) &&
                        ((g.Geometry is MapPoint) && (g.Geometry as MapPoint).Equals(graphic.Geometry as MapPoint)) ||
                        ((g.Geometry is Envelope) && (g.Geometry as Envelope).Equals(graphic.Geometry as Envelope)) ||
                        ((g.Geometry is Polygon) && (g.Geometry as Polygon).Equals(graphic.Geometry as Polygon)) ||
                        ((g.Geometry is MultiPoint) && (g.Geometry as MultiPoint).Equals(graphic.Geometry as MultiPoint)) ||
                        ((g.Geometry is Polyline) && (g.Geometry as Polyline).Equals(graphic.Geometry as Polyline)) ||
                            g.Geometry.Equals(graphic.Geometry));
                if (graphicToRemove != null)
                {
                    Layer.Graphics.Remove(graphicToRemove);
                }

I have to check every single type of Geometry. I should be able to do the following:
Graphic graphicToRemove = Layer.Graphics.FirstOrDefault(g =>
                        (g.Geometry != null) && g.Geometry.Equals(graphic.Geometry));

If a new type gets added, I then have to change my code to account for the new type.