Return this as inherited type

Question

I am creating a finite state machine class, but am running into some trouble returning this as the correct type.

The parent class

public class FsmState<StateAsEnum, SelfClass> where StateAsEnum : Enum
{
    protected SelfClass NextState;

    public StateAsEnum StateName { get; protected set; }

    public NpcState Process()
    {
        if (Stage == FsmStage.Enter) Enter();
        if (Stage == FsmStage.Update) StateUpdate();

        if (Stage == FsmStage.Exit)
        {
            Exit();
            return NextState;
        }

        return this; //the trouble.
    }
}

I can not ensure that SelfClass and the type FsmState are the same. When I inherit from this class I would like to return this as the inherited class.

class NpcState : FsmState<NpcState.States, NpcState>
{
     Process();
}

This guy is used in

NpcState currentState 

loop 
{
      currentState = currentState.Process();
}

Answer 1

Okay I figured it out. It doesn't look nice but the casting helped when I applied recursive inheritance on the types.

public class FsmState<StateAsEnum, SelfClass> where StateAsEnum : Enum where SelfClass : FsmState<StateAsEnum,SelfClass>

public SelfClass Process()
    {
        ...
    
        return (SelfClass) this;
    }

It's not pretty but it works.