public static bool ReferenceEquals( object left, object right );
public static bool Equals( object left, object right );
public virtual bool Equals( object right);
public static bool operator==( MyClass left, MyClass right );

 1 public static bool Equals( object left, object right )
 2 {
 3   // Check object identity
 4    if (left == right )
 5     return true;
 6   // both null references handled above
 7   if ((left == null) || (right == null))
 8     return false;
 9   return left.Equals (right);
10 }

 1 public class Foo
 2 {
 3   public override bool Equals( object right )
 4   {
 5     // check null:
 6     // the this pointer is never null in C# methods.
 7     if (right == null)
 8       return false;
 9 
10     if (object.ReferenceEquals( this, right ))
11       return true;
12 
13     // Discussed below.
14     if (this.GetType() != right.GetType())
15       return false;
16 
17     // Compare this type's contents here:
18     return CompareFooMembers(
19       this, right as Foo );
20   }
21 }
22 
23 

 1 public class B
 2 {
 3   public override bool Equals( object right )
 4   {
 5     // check null:
 6     if (right == null)
 7       return false;
 8 
 9     // Check reference equality:
10     if (object.ReferenceEquals( this, right ))
11       return true;
12 
13     // Problems here, discussed below.
14     B rightAsB = right as B;
15     if (rightAsB == null)
16       return false;
17 
18     return CompareBMembers( this, rightAsB );
19   }
20 }
21 
22 public class D : B
23 {
24   // etc.
25   public override bool Equals( object right )
26   {
27     // check null:
28     if (right == null)
29       return false;
30 
31     if (object.ReferenceEquals( this, right ))
32       return true;
33 
34     // Problems here.
35     D rightAsD = right as D;
36     if (rightAsD == null)
37       return false;
38 
39     if (base.Equals( rightAsD ) == false)
40       return false;
41 
42     return CompareDMembers( this, rightAsD );
43   }
44 
45 }
46 
47 //Test:
48 B baseObject = new B();
49 D derivedObject = new D();
50 
51 // Comparison 1.
52 if (baseObject.Equals(derivedObject))
53   Console.WriteLine( "Equals" );
54 else
55   Console.WriteLine( "Not Equal" );
56 
57 // Comparison 2.
58 if (derivedObject.Equals(baseObject))
59   Console.WriteLine( "Equals" );
60 else
61   Console.WriteLine( "Not Equal" );
62 
63