mcs/tests/gtest-variance-5.cs

   1 // Compiler options: -langversion:future
   2
   3 interface ICovariant<out T>
   4 {
   5         T Foo { get; }
   6 }
   7
   8 interface IContravariant<in T>
   9 {
  10         int Bar (T bar);
  11 }
  12
  13 interface IBothVariants <out T1, in T2> : ICovariant<T1>, IContravariant<T2>
  14 {
  15 }
  16
  17 interface IInvariant <T> : ICovariant<T>, IContravariant<T>
  18 {
  19 }
  20
  21 class BothVariants <T1, T2> : IBothVariants <T1, T2>
  22 {
  23         public BothVariants (T1 foo)
  24         {
  25                 Foo = foo;
  26         }
  27
  28         public T1 Foo { get; private set; }
  29
  30         public int Bar (T2 bar)
  31         {
  32                 return bar.GetHashCode () ^ Foo.GetHashCode ();
  33         }
  34 }
  35
  36 class Invariant <T> : IInvariant<T> where T : new()
  37 {
  38         public T Foo { get { return new T (); } }
  39
  40         public int Bar (T bar)
  41         {
  42                 return bar.GetHashCode ();
  43         }
  44 }
  45
  46 class A
  47 {
  48         public virtual string Fruit { get { return "Apple"; } }
  49 }
  50
  51 class B : A
  52 {
  53         public override string Fruit { get { return "Banana"; } }
  54 }
  55
  56 class C : B
  57 {
  58         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"; } }
  59 }
  60
  61 public class Test
  62 {
  63         static int Main ()
  64         {
  65                 var b = new B ();
  66                 var c = new C ();
  67
  68                 IBothVariants<A, C> both = new BothVariants<B,B> (b);
  69
  70                 if (both.Bar (c) != (b.GetHashCode () ^ c.GetHashCode ()))
  71                         return 1;
  72
  73                 IInvariant<B> neither = new Invariant<B> ();
  74                 ICovariant<A> co = neither;
  75                 if (co.Foo.Fruit != "Banana")
  76                         return 2;
  77
  78                 IContravariant<C> contra = neither;
  79                 if (contra.Bar (c) != c.GetHashCode ())
  80                         return 3;
  81
  82                 return 0;
  83         }
  84 }