using Godot;

public abstract class SingletonAutoLoad<T> : Node where T : Node
{
    private static T instance;
    public static T Instance => instance;

    public override void _Ready()
    {
        if (instance != null)
        {
            GD.PrintErr("SingletonManager: " + typeof(T).Name + " already exists!");
            return;
        }

        instance = this as T;
        AfterInit();
    }

    public virtual void AfterInit()
    {
    }
}

public class ConcreteAutoLoadThing: SingletonAutoLoad<ConcreteAutoLoadThing>
{
    public override void AfterInit()
    {
        // my ready logic without touching the singleton initialization
    }
}