Covariance

Covariance

namespace CovarianceTests
{
    using System.Collections.Generic;
    using NUnit.Framework;

    public class CovarianceTests
    {
        [Test]
        public void IEnumerableT_Is_Covariant()
        {
            var list = new[] {new C1()};
            //var list = new[] {new C1()}.ToList(); will not compile!

            var b = new B
                {
                    List = list
                };

            Do(b);
        }

        private static void Do(A a)
        {
            Assert.IsTrue(a.List[0].Val);
        }
    }

    public class A
    {
        public IList<C> List { get; set; }
    }

    public class B : A
    { }

    public class C
    {
        public virtual bool Val { get { return false; } }
    }

    public class C1 : C
    {
        public override bool Val { get { return true; } }
    }
}