Output

a:
b:
setting a = a1
a: a1
b:
setting b = b1
a: a1
b: b1
setting a = b1
a: a2
b: b1
setting b = b2
a: a2
b: b2

Program.cs

    class Program {
        static void Main(string[] args) {
            WriteValues();

            Console.WriteLine("setting a = a1");
            Foo<int>.SharedValue = "a1";

            WriteValues();

            Console.WriteLine("setting b = b1");
            Foo<string>.SharedValue = "b1";

            WriteValues();

            Console.WriteLine("setting a = a2");
            Foo<int>.SharedValue = "a2";

            WriteValues();

            Console.WriteLine("setting b = b2");
            Foo<string>.SharedValue = "b2";

            WriteValues();
        }

        private static void WriteValues() {
            Console.WriteLine("a: {0}", Foo<int>.SharedValue);
            Console.WriteLine("b: {0}", Foo<string>.SharedValue);
        }
    }

    internal class Foo<T> {
        public static string SharedValue = "";
    }