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interface ICovariant<out T>
{
T Foo { get; }
}
interface IContravariant<in T>
{
int Bar (T bar);
}
interface IBothVariants <out T1, in T2> : ICovariant<T1>, IContravariant<T2>
{
}
interface IInvariant <T> : ICovariant<T>, IContravariant<T>
{
}
class BothVariants <T1, T2> : IBothVariants <T1, T2>
{
public BothVariants (T1 foo)
{
Foo = foo;
}
public T1 Foo { get; private set; }
public int Bar (T2 bar)
{
return bar.GetHashCode () ^ Foo.GetHashCode ();
}
}
class Invariant <T> : IInvariant<T> where T : new()
{
public T Foo { get { return new T (); } }
public int Bar (T bar)
{
return bar.GetHashCode ();
}
}
class A
{
public virtual string Fruit { get { return "Apple"; } }
}
class B : A
{
public override string Fruit { get { return "Banana"; } }
}
class C : B
{
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"; } }
}
public class Test
{
public static int Main ()
{
var b = new B ();
var c = new C ();
IBothVariants<A, C> both = new BothVariants<B,B> (b);
if (both.Bar (c) != (b.GetHashCode () ^ c.GetHashCode ()))
return 1;
IInvariant<B> neither = new Invariant<B> ();
ICovariant<A> co = neither;
if (co.Foo.Fruit != "Banana")
return 2;
IContravariant<C> contra = neither;
if (contra.Bar (c) != c.GetHashCode ())
return 3;
return 0;
}
}
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