Creating an instance of an open generic type without specifying a type argument

  • Article

My fellow Roslyn tester @vreshetnikov has found not one, but two ways to do the impossible:

1:

 using System;
 
class Program
{
    static void Main()
    {
        var open = Enum.ToObject(typeof(C<>.E), 0);
        Console.WriteLine(open.GetType());
    }
}
 
class C<T>
{
    public enum E { }
}

2:

 using System;<br> <br>class Program<br>{<br>    static void Main()<br>    {<br>        Action<C<int>.E> a = M;<br>        var open = a.Method.GetGenericMethodDefinition().GetParameters()[0].DefaultValue;<br>        Console.WriteLine(open.GetType());<br>    }<br> <br>    static void M<T>(C<T>.E e = 0) { }<br>}<br> <br>class C<T><br>{<br>    public enum E { }<br>}