namespace ValueEquality
{
using System;
class TwoDPoint : IEquatable<TwoDPoint>
{
// Readonly auto-implemented properties.
public int X { get; private set; }
public int Y { get; private set; }
// Set the properties in the constructor.
public TwoDPoint(int x, int y)
{
if ((x < 1) || (x > 2000) || (y < 1) || (y > 2000))
throw new System.ArgumentException("Point must be in range 1 - 2000");
this.X = x;
this.Y = y;
}
public override bool Equals(object obj)
{
return this.Equals(obj as TwoDPoint);
}
public bool Equals(TwoDPoint p)
{
// If parameter is null, return false.
if (Object.ReferenceEquals(p, null))
{
return false;
}
// Optimization for a common success case.
if (Object.ReferenceEquals(this, p))
{
return true;
}
// If run-time types are not exactly the same, return false.
if (this.GetType() != p.GetType())
return false;
// Return true if the fields match.
// Note that the base class is not invoked because it is
// System.Object, which defines Equals as reference equality.
return (X == p.X) && (Y == p.Y);
}
public override int GetHashCode()
{
return X * 0x00010000 + Y;
}
public static bool operator ==(TwoDPoint lhs, TwoDPoint rhs)
{
// Check for null on left side.
if (Object.ReferenceEquals(lhs, null))
{
if (Object.ReferenceEquals(rhs, null))
{
// null == null = true.
return true;
}
// Only the left side is null.
return false;
}
// Equals handles case of null on right side.
return lhs.Equals(rhs);
}
public static bool operator !=(TwoDPoint lhs, TwoDPoint rhs)
{
return !(lhs == rhs);
}
}
// For the sake of simplicity, assume a ThreeDPoint IS a TwoDPoint.
class ThreeDPoint : TwoDPoint, IEquatable<ThreeDPoint>
{
public int Z { get; private set; }
public ThreeDPoint(int x, int y, int z)
: base(x, y)
{
if ((z < 1) || (z > 2000))
throw new System.ArgumentException("Point must be in range 1 - 2000");
this.Z = z;
}
public override bool Equals(object obj)
{
return this.Equals(obj as ThreeDPoint);
}
public bool Equals(ThreeDPoint p)
{
// If parameter is null, return false.
if (Object.ReferenceEquals(p, null))
{
return false;
}
// Optimization for a common success case.
if(Object.ReferenceEquals(this, p))
{
return true;
}
// Check properties that this class declares.
if (Z == p.Z)
{
// Let base class check its own fields
// and do the run-time type comparison.
return base.Equals((TwoDPoint)p);
}
else
return false;
}
public override int GetHashCode()
{
return (X * 0x100000) + (Y * 0x1000) + Z;
}
public static bool operator ==(ThreeDPoint lhs, ThreeDPoint rhs)
{
// Check for null.
if (Object.ReferenceEquals(lhs, null))
{
if (Object.ReferenceEquals(lhs, null))
{
// null == null = true.
return true;
}
// Only the left side is null.
return false;
}
// Equals handles the case of null on right side.
return lhs.Equals(rhs);
}
public static bool operator !=(ThreeDPoint lhs, ThreeDPoint rhs)
{
return !(lhs == rhs);
}
}
class Program
{
static void Main(string[] args)
{
ThreeDPoint pointA = new ThreeDPoint(3, 4, 5);
ThreeDPoint pointB = new ThreeDPoint(3, 4, 5);
ThreeDPoint pointC = null;
int i = 5;
Console.WriteLine("pointA.Equals(pointB) = {0}", pointA.Equals(pointB));
Console.WriteLine("pointA == pointB = {0}", pointA == pointB);
Console.WriteLine("null comparison = {0}", pointA.Equals(pointC));
Console.WriteLine("Compare to some other type = {0}", pointA.Equals(i));
TwoDPoint pointD = null;
TwoDPoint pointE = null;
Console.WriteLine("Two null TwoDPoints are equal: {0}", pointD == pointE);
pointE = new TwoDPoint(3, 4);
Console.WriteLine("(pointE == pointA) = {0}", pointE == pointA);
Console.WriteLine("(pointA == pointE) = {0}", pointA == pointE);
Console.WriteLine("(pointA != pointE) = {0}", pointA != pointE);
System.Collections.ArrayList list = new System.Collections.ArrayList();
list.Add(new ThreeDPoint(3, 4, 5));
Console.WriteLine("pointE.Equals(list[0]): {0}", pointE.Equals(list[0]));
// Keep the console window open in debug mode.
System.Console.WriteLine("Press any key to exit.");
System.Console.ReadKey();
}
}
/* Output:
pointA.Equals(pointB) = True
pointA == pointB = True
null comparison = False
Compare to some other type = False
Two null TwoDPoints are equal: True
(pointE == pointA) = False
(pointA == pointE) = False
(pointA != pointE) = True
pointE.Equals(list[0]): False
*/
}