mcs/tests/gtest-variance-5.cs

   1 interface ICovariant<out T>
   2 {
   3         T Foo { get; }
   4 }
   5
   6 interface IContravariant<in T>
   7 {
   8         int Bar (T bar);
   9 }
  10
  11 interface IBothVariants <out T1, in T2> : ICovariant<T1>, IContravariant<T2>
  12 {
  13 }
  14
  15 interface IInvariant <T> : ICovariant<T>, IContravariant<T>
  16 {
  17 }
  18
  19 class BothVariants <T1, T2> : IBothVariants <T1, T2>
  20 {
  21         public BothVariants (T1 foo)
  22         {
  23                 Foo = foo;
  24         }
  25
  26         public T1 Foo { get; private set; }
  27
  28         public int Bar (T2 bar)
  29         {
  30                 return bar.GetHashCode () ^ Foo.GetHashCode ();
  31         }
  32 }
  33
  34 class Invariant <T> : IInvariant<T> where T : new()
  35 {
  36         public T Foo { get { return new T (); } }
  37
  38         public int Bar (T bar)
  39         {
  40                 return bar.GetHashCode ();
  41         }
  42 }
  43
  44 class A
  45 {
  46         public virtual string Fruit { get { return "Apple"; } }
  47 }
  48
  49 class B : A
  50 {
  51         public override string Fruit { get { return "Banana"; } }
  52 }
  53
  54 class C : B
  55 {
  56         public override string Fruit { get { return "Carrot which I know is not a fruit but you better shut up about it before I cut you"; } }
  57 }
  58
  59 public class Test
  60 {
  61         public static int Main ()
  62         {
  63                 var b = new B ();
  64                 var c = new C ();
  65
  66                 IBothVariants<A, C> both = new BothVariants<B,B> (b);
  67
  68                 if (both.Bar (c) != (b.GetHashCode () ^ c.GetHashCode ()))
  69                         return 1;
  70
  71                 IInvariant<B> neither = new Invariant<B> ();
  72                 ICovariant<A> co = neither;
  73                 if (co.Foo.Fruit != "Banana")
  74                         return 2;
  75
  76                 IContravariant<C> contra = neither;
  77                 if (contra.Bar (c) != c.GetHashCode ())
  78                         return 3;
  79
  80                 return 0;
  81         }
  82 }