How to make a generic singleton base class C# [duplicate]

Answer 1

I would avoid this kind of recursive generic pattern. Read this this blog post for a detailed explanation of the pattern and reasons not to use it.

As far as I can tell, you don't need to have any sub-classes of SingletonBase<T>. I can't see anything that a subclass of SingletonBase<T> would be able to add to your code. I would simply rewrite it as

public static class Singleton<T> where T : class, new()
{
    ...
}

You can then use it as

var test = Singleton<Test>.Instance;

If you want to be able to use Test as a singleton, create it as

public class Test 
{
    public static T Instance
    {
        get { return Singleton.Instance<Test>; }
    }
}

Answer 2

The problem is your generic constraint where T : class, new(). The new() constraint requires a public, parameterless constructor on T. There is no way around this; you need to provide such a constructor in Permission Controller.