Here's my problem. I've got generic Singleton class like this :

public abstract class Singleton<T> where T : Singleton<T>, new()
{
    private static T instance;
    public static T Instance
    {
        get
        {
            return instance == null ? new T() : instance;
        }
    }
}

And I wanna create a ProcessManager also is an generic abstract class but with enum generic parameter that inherit from this Singleton class. This is the code that currently I've made but with error:

    public abstract class ProcessManager<TEnum> : Singleton<ProcessManager<TEnum>> where TEnum : Enum, new()
    {
        private TEnum state;
        private Dictionary<TEnum, Action> stateInitializations = new Dictionary<TEnum, Action>();

        public TEnum State
        {
            get { return state; }
            set { InitializeState(state); }
        }

        private void InitializeState(TEnum _state)
        {
            stateInitializations[_state].Invoke();
        }
    }

There is a red underline at 'class ProcessManager' with error CS0310:

ProcessManager<TEnum> must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'parameter' in the generic type or method Singleton<T>

Anyone could tell me how to fix this plz?

CodePudding user response：

Since T is a recursive constraint, you have to force any type that extends ProcessManager to map their concrete type onto T;

abstract class ProcessManager<T, E> : Singleton<T>
    where T : ProcessManager<T, E>, new()
    where E : Enum { ... }

class ConcreteType : ProcessManager<ConcreteType, EnumType> { ... }

CodePudding user response：

I tried two way to solve this problem:

1. Remove ProcessManager's 'abstract'.
2. Remove Singleton's ', new()' and also new T.

But second one doesn't make sense,, so I finally decided to use first one..

Anyway really thanks for those nice people who leave comment tried to help me sincerely.