DDWiki/分享/后端/DDD/6、强类型枚举.md

```
<PackageReference Include="Ardalis.SmartEnum" Version="2.0.0" />
```



```
    /// <summary>
    /// 枚举作为状态机
    /// </summary>
    public abstract class ReservationStatus : SmartEnum<ReservationStatus>
    {
        private ReservationStatus(string name, int value) : base(name, value) { }

        public abstract bool CanTransitionTo(ReservationStatus next);

        public static readonly ReservationStatus New = new NewStatus();
        public static readonly ReservationStatus Accepted = new AcceptedStatus();
        public static readonly ReservationStatus Paid = new PaidStatus();
        public static readonly ReservationStatus Cancelled = new CancelledStatus();

        private sealed class NewStatus : ReservationStatus
        {
            public NewStatus() : base("New", 0)
            {
            }

            public override bool CanTransitionTo(ReservationStatus next) =>
                next == ReservationStatus.Accepted || next == ReservationStatus.Cancelled;
        }

        private sealed class AcceptedStatus : ReservationStatus
        {
            public AcceptedStatus() : base("Accepted", 1)
            {
            }

            public override bool CanTransitionTo(ReservationStatus next) =>
                next == ReservationStatus.Paid || next == ReservationStatus.Cancelled;
        }

        private sealed class PaidStatus : ReservationStatus
        {
            public PaidStatus() : base("Paid", 2)
            {
            }

            public override bool CanTransitionTo(ReservationStatus next) =>
                next == ReservationStatus.Cancelled;
        }

        private sealed class CancelledStatus : ReservationStatus
        {
            public CancelledStatus() : base("Cancelled", 3)
            {
            }

            public override bool CanTransitionTo(ReservationStatus next) =>
                false;
        }


    }

    /// <summary>
    /// 枚举可以初始化
    /// </summary>
    public sealed class TestEnum : SmartEnum<TestEnum>
    {
       private TestEnum(string name, int value) : base(name, value)
        {

        }

        public static readonly TestEnum One = new TestEnum(nameof(One), 1);
        public static readonly TestEnum Two = new TestEnum(nameof(Two), 2);
        public static readonly TestEnum Three = new TestEnum(nameof(Three), 3);
    }

    /// <summary>
    /// 别名
    /// </summary>
    public sealed class TestEnum1 : SmartEnum<TestEnum1>
    {
        //真实的值通过构造函数来设定
        private TestEnum1(string name, ushort value) : base(name, value) { }

        /// <summary>
        /// One看作是别名
        /// </summary>
        public static readonly TestEnum1 One = new TestEnum1("a", 1);
        public static readonly TestEnum1 Two = new TestEnum1("b", 2);
        public static readonly TestEnum1 Three = new TestEnum1("a", 3);
    }

    /// <summary>
    /// 枚举也可以被继承
    /// 也可以是抽象
    /// </summary>
    public abstract class EmployeeType : SmartEnum<EmployeeType>
    {
        private EmployeeType(string name, int value):base(name, value) { }
        public abstract decimal BonusSize { get; }

        public static readonly EmployeeType Manager = new ManagerType();
        public static readonly EmployeeType Assistant = new AssistantType();

        
        private sealed class ManagerType : EmployeeType
        {
            public ManagerType():base("Manager",1)
            {

            }

            public override decimal BonusSize => 10m;
        }

        private sealed class AssistantType : EmployeeType
        {
            public AssistantType() : base("Assistant",2)
            {

            }

            public override decimal BonusSize => 20m;
        }
    }
```