"Static" Abstract Classes

Program.cs

using System;

static class Program
{
    static void Main()
    {
        A.Method();
        new B().Method();

        A.Method();
        new B().Method();
    }
}

sealed class A : Template.Static<A.Instance>
{
    internal sealed class Instance : Template.Instance<Instance>
    {
        internal override string String => nameof(A);
    }
}

sealed class B : Template
{
    internal override string String => nameof(B);
}

abstract class Template
{
    internal abstract string String { get; }

    internal void Method() => Console.WriteLine(String);

    internal abstract class Instance<T> : Template where T : Instance<T>, new()
    {
        public Instance() => Console.WriteLine(typeof(Instance<T>));

        internal static readonly T s_this = new();
    }

    internal abstract class Static<T> where T : Instance<T>, new()
    {
        public Static() => Console.WriteLine(typeof(Static<T>));

        static readonly T s_this = Instance<T>.s_this;

        internal static string String => s_this.String;

        internal static void Method() => s_this.Method();
    }
}