badarray.cs

using System;

class A {}
class B : A {}

class Badarray
{
    static void Main(string[] args) 
    {
        var x = new A[2];
        x[0] = new A(); // good, yes?
        x[1] = new B(); // also useful
        Ohno(x); //despite the name this is fine

        var y = new B[1]; //but now..
        x[0] = new B(); //perfectly legitimate; however:
        Ohno(y); //oh no
    }

    static void Ohno(A[] thisArrayContainsAs)
    {
        Console.WriteLine(thisArrayContainsAs[0]); //fine 
        thisArrayContainsAs[0] = new A(); //OH NO
    }
}