我想继承单例模式，怎么办

Question

单例模式怎么继承，我一个一个写不安全也更复杂，但是我不知道要怎么继承。

Answer 1

public abstract class BaseSingleton<T> where T : BaseSingleton<T>
{
    private static BaseSingleton<T>? _instance;

    public static BaseSingleton<T> Instance => _instance ?? throw new InvalidOperationException("instance not created");

    protected BaseSingleton()
    {
        //if(_instance is not null)
        //{
        //    throw new InvalidOperationException("instance already created");
        //}
        _instance ??= this;
    }
}

public class SingletonClass1 : BaseSingleton<SingletonClass1>
{
    public SingletonClass1() 
    {
    }
}

public class SingletonClass2 : BaseSingleton<SingletonClass2>
{
    public SingletonClass2() 
    {
    }
}


public class Singleton1
{
    public static Singleton1 Instance => SingletonHelper<Singleton1>.GetInstance();
    public Singleton1()
    {
    }

}

public class Singleton2
{
    public static Singleton2 Instance => SingletonHelper<Singleton2>.GetInstance(() => new Singleton2());

    public Singleton2()
    {
    }

}

public static class SingletonHelper<T> where T : class
{
    private static readonly object _lock = new();
    private static T? _instance;

    public static T GetInstance(Func<T>? func = null)
    {
        if (_instance is null)
        {
            lock (_lock)
            {
                func ??= Activator.CreateInstance<T>;
                _instance ??= func();
            }
        }
        return _instance;
    }
}