static ctor.cs

using System;

namespace StaticTest
{
    public class Program
    {
        public static void Main(string[] args)
        {
            //args are empty but .NET and MONO will init Foo anyway, .NET core - won't.
            var obj = args.Length > 0 ? Foo.Instance : null;
            Console.WriteLine(obj);
        }
    }

    public class Foo
    {
        public static Foo Instance = new Foo();

        //static Foo() {}

        public Foo()
        {
            Console.WriteLine("Foo init.");
        }
    }
}