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创建枚举类型

编程语言通常提供语法来声明一个由一组命名常量及其值组成的枚举。以下示例说明了 C#、F# 和 Visual Basic 用于定义枚举的语法。它创建一个名为具有 ArrivalStatus 三个成员的枚举： ArrivalStatus.Early 、 ArrivalStatus.OnTime 和 ArrivalStatus.Late 。请注意，在所有情况下，枚举都不会显式继承; Enum 继承关系由编译器隐式处理。
public enum ArrivalStatus { Unknown=-3, Late=-1, OnTime=0, Early=1 };
type ArrivalStatus =
    | Late = -1
    | OnTime = 0
    | Early = 1
Public Enum ArrivalStatus1 As Integer
    Late = -1
    OnTime = 0
    Early = 1
End Enum
不应创建基础类型为非整型或 Char。 尽管可以使用反射创建此类枚举类型，但使用生成的类型的方法调用不可靠，也可能会引发其他异常。
实例化枚举类型
可以实例化枚举类型，就像实例化任何其他值类型一样：通过声明变量并向其分配枚举的常量之一。 下面的示例实例化 ArrivalStatus 其值为 ArrivalStatus.OnTime.
public class Example
   public static void Main()
      ArrivalStatus status = ArrivalStatus.OnTime;
      Console.WriteLine("Arrival Status: {0} ({0:D})", status);
// The example displays the following output:
//       Arrival Status: OnTime (0)
let status = ArrivalStatus.OnTime
printfn $"Arrival Status: {status} ({status:D})"
// The example displays the following output:
//       Arrival Status: OnTime (0)
Public Module Example1
    Public Sub Main()
        Dim status As ArrivalStatus1 = ArrivalStatus1.OnTime
        Console.WriteLine("Arrival Status: {0} ({0:D})", status)
    End Sub
End Module
' The example displays the following output:
'        Arrival Status: OnTime (0)
还可以通过以下方式实例化枚举值：
通过使用特定编程语言的功能（如 C# 中所示）或将整数值转换为枚举值（如在 Visual Basic 中）。 以下示例创建一个 ArrivalStatus 对象，其值 ArrivalStatus.Early 采用这种方式。
ArrivalStatus status2 = (ArrivalStatus)1;
Console.WriteLine("Arrival Status: {0} ({0:D})", status2);
// The example displays the following output:
//       Arrival Status: Early (1)
let status2 = enum<ArrivalStatus> 1
printfn $"Arrival Status: {status2} ({status2:D})"
// The example displays the following output:
//       Arrival Status: Early (1)
Dim status2 As ArrivalStatus2 = CType(1, ArrivalStatus2)
Console.WriteLine("Arrival Status: {0} ({0:D})", status2)
' The example displays the following output:
'       Arrival Status: Early (1)
通过调用其隐式无参数构造函数。 如以下示例所示，在这种情况下，枚举实例的基础值为 0。 但是，这不一定是枚举中有效常量的值。
ArrivalStatus status1 = new ArrivalStatus();
Console.WriteLine("Arrival Status: {0} ({0:D})", status1);
// The example displays the following output:
//       Arrival Status: OnTime (0)
let status1 = ArrivalStatus()
printfn $"Arrival Status: {status1} ({status1:D})"
// The example displays the following output:
//       Arrival Status: OnTime (0)
Dim status1 As New ArrivalStatus2()
Console.WriteLine("Arrival Status: {0} ({0:D})", status1)
' The example displays the following output:
'        Arrival Status: OnTime (0)
通过调用 Parse 或 TryParse 方法分析包含枚举中常量名称的字符串。 有关详细信息，请参阅 “分析枚举值 ”部分。
通过调用 ToObject 方法将整型值转换为枚举类型。 有关详细信息，请参阅“ 执行转换 ”部分。
枚举最佳做法
建议在定义枚举类型时使用以下最佳做法：
如果尚未定义值为 0 的枚举成员，请考虑创建 None 枚举常量。 默认情况下，用于枚举的内存由公共语言运行时初始化为零。 因此，如果未定义值为零的常量，则枚举将在创建时包含非法值。
如果应用程序必须表示一个明显的默认情况，请考虑使用枚举常量，其值为零来表示它。 如果没有默认情况，请考虑使用值为零的枚举常量来指定其他任何枚举常量未表示的情况。
请勿指定为将来使用保留的枚举常量。
定义将枚举常量作为值的方法或属性时，请考虑验证该值。 原因是，即使枚举中未定义数值，也可以将数值强制转换为枚举类型。
有关常量是位字段的枚举类型的其他最佳做法，请参阅 “非独占成员”和“Flags 属性 ”部分。
使用枚举执行操作
创建枚举时无法定义新方法。 但是，枚举类型从 Enum 类继承一组完整的静态和实例方法。 以下部分调查了其中大多数方法，以及处理枚举值时常用的其他几种方法。
可以使用强制转换（在 C# 和 F# 中）或转换（在 Visual Basic 中）运算符在枚举成员及其基础类型之间进行转换。 在 F# 中， enum 也使用该函数。 以下示例使用强制转换或转换运算符执行从整数到枚举值和从枚举值到整数的转换。
int value3 = 2;
ArrivalStatus status3 = (ArrivalStatus)value3;
int value4 = (int)status3;
let value3 = 2
let status3 = enum<ArrivalStatus> value3
let value4 = int status3
Dim value3 As Integer = 2
Dim status3 As ArrivalStatus2 = CType(value3, ArrivalStatus2)
Dim value4 As Integer = CInt(status3)
该 Enum 类还包括将 ToObject 任何整型类型的值转换为枚举值的方法。 以下示例使用ToObject(Type, Int32)该方法将值Int32ArrivalStatus转换为值。 请注意，由于 ToObject 返回类型的 Object值，使用强制转换或转换运算符仍可能需要将对象强制转换为枚举类型。
int number = -1;
ArrivalStatus arrived = (ArrivalStatus)ArrivalStatus.ToObject(typeof(ArrivalStatus), number);
let number = -1
let arrived = ArrivalStatus.ToObject(typeof<ArrivalStatus>, number) :?> ArrivalStatus
Dim number As Integer = -1
Dim arrived As ArrivalStatus2 = CType(ArrivalStatus2.ToObject(GetType(ArrivalStatus2), number), ArrivalStatus2)
将整数转换为枚举值时，可以分配一个实际上不是枚举成员的值。 若要防止这种情况，可以在执行转换之前将整数传递给 IsDefined 方法。 下面的示例使用此方法来确定整数值数组中的元素是否可以转换为 ArrivalStatus 值。
using System;
public class Example3
    public static void Main()
        int[] values = { -3, -1, 0, 1, 5, Int32.MaxValue };
        foreach (var value in values)
            ArrivalStatus status;
            if (Enum.IsDefined(typeof(ArrivalStatus), value))
                status = (ArrivalStatus)value;
                status = ArrivalStatus.Unknown;
            Console.WriteLine("Converted {0:N0} to {1}", value, status);
// The example displays the following output:
//       Converted -3 to Unknown
//       Converted -1 to Late
//       Converted 0 to OnTime
//       Converted 1 to Early
//       Converted 5 to Unknown
//       Converted 2,147,483,647 to Unknown
open System
type ArrivalStatus =
    | Unknown = -3
    | Late = -1
    | OnTime = 0
    | Early = 1
let values = [ -3; -1; 0; 1; 5; Int32.MaxValue ]
for value in values do
    let status =
        if Enum.IsDefined(typeof<ArrivalStatus>, value) then
            enum value
            ArrivalStatus.Unknown
    printfn $"Converted {value:N0} to {status}"
// The example displays the following output:
//       Converted -3 to Unknown
//       Converted -1 to Late
//       Converted 0 to OnTime
//       Converted 1 to Early
//       Converted 5 to Unknown
//       Converted 2,147,483,647 to Unknown
Public Enum ArrivalStatus4 As Integer
    Unknown = -3
    Late = -1
    OnTime = 0
    Early = 1
End Enum
Module Example4
    Public Sub Main()
        Dim values() As Integer = {-3, -1, 0, 1, 5, Int32.MaxValue}
        For Each value In values
            Dim status As ArrivalStatus4
            If [Enum].IsDefined(GetType(ArrivalStatus4), value) Then
                status = CType(value, ArrivalStatus4)
                status = ArrivalStatus4.Unknown
            End If
            Console.WriteLine("Converted {0:N0} to {1}", value, status)
    End Sub
End Module
' The example displays the following output:
'       Converted -3 to Unknown
'       Converted -1 to Late
'       Converted 0 to OnTime
'       Converted 1 to Early
'       Converted 5 to Unknown
'       Converted 2,147,483,647 to Unknown
尽管该 Enum 类提供了接口的 IConvertible 显式接口实现，以便从枚举值转换为整型类型，但应使用类的方法 Convert （例如 ToInt32）执行这些转换。 下面的示例演示如何使用 GetUnderlyingType 该方法以及 Convert.ChangeType 方法将枚举值转换为其基础类型。 请注意，此示例不需要在编译时知道枚举的基础类型。
ArrivalStatus status = ArrivalStatus.Early;
var number = Convert.ChangeType(status, Enum.GetUnderlyingType(typeof(ArrivalStatus)));
Console.WriteLine("Converted {0} to {1}", status, number);
// The example displays the following output:
//       Converted Early to 1
let status = ArrivalStatus.Early
let number = Convert.ChangeType(status, Enum.GetUnderlyingType typeof<ArrivalStatus>)
printfn $"Converted {status} to {number}"
// The example displays the following output:
//       Converted Early to 1
Dim status As ArrivalStatus5 = ArrivalStatus5.Early
Dim number = Convert.ChangeType(status, [Enum].GetUnderlyingType(GetType(ArrivalStatus5)))
Console.WriteLine("Converted {0} to {1}", status, number)
' The example displays the following output:
'       Converted Early to 1
分析枚举值
使用 Parse 和 TryParse 方法可以将枚举值的字符串表示形式转换为该值。 字符串表示形式可以是枚举常量的名称或基础值。 请注意，如果字符串可以转换为枚举的基础类型的值，则分析方法将成功转换不是特定枚举成员的数字的字符串表示形式。 为防止出现这种情况， IsDefined 可以调用该方法以确保分析方法的结果是有效的枚举值。 此示例演示了此方法，并演示了对 Parse(Type, String) 该方法和 Enum.TryParse<TEnum>(String, TEnum) 方法的调用。 请注意，非泛型分析方法返回一个对象，该对象可能需要强制转换（在 C# 和 F# 中）或将（在 Visual Basic 中）转换为适当的枚举类型。
string number = "-1";
string name = "Early";
    ArrivalStatus status1 = (ArrivalStatus)Enum.Parse(typeof(ArrivalStatus), number);
    if (!(Enum.IsDefined(typeof(ArrivalStatus), status1)))
        status1 = ArrivalStatus.Unknown;
    Console.WriteLine("Converted '{0}' to {1}", number, status1);
catch (FormatException)
    Console.WriteLine("Unable to convert '{0}' to an ArrivalStatus value.",
                      number);
ArrivalStatus status2;
if (Enum.TryParse<ArrivalStatus>(name, out status2))
    if (!(Enum.IsDefined(typeof(ArrivalStatus), status2)))
        status2 = ArrivalStatus.Unknown;
    Console.WriteLine("Converted '{0}' to {1}", name, status2);
    Console.WriteLine("Unable to convert '{0}' to an ArrivalStatus value.",
                      number);
// The example displays the following output:
//       Converted '-1' to Late
//       Converted 'Early' to Early
let number = "-1"
let name = "Early"
    let status1 = Enum.Parse(typeof<ArrivalStatus>, number) :?> ArrivalStatus
    let status1 =
        if not (Enum.IsDefined(typeof<ArrivalStatus>, status1) ) then
            ArrivalStatus.Unknown
            status1
    printfn $"Converted '{number}' to {status1}"
with :? FormatException ->
    printfn $"Unable to convert '{number}' to an ArrivalStatus value."
match Enum.TryParse<ArrivalStatus> name with
| true, status2 ->
    let status2 = 
        if not (Enum.IsDefined(typeof<ArrivalStatus>, status2) ) then
            ArrivalStatus.Unknown
            status2
    printfn $"Converted '{name}' to {status2}"
| _ ->
    printfn $"Unable to convert '{number}' to an ArrivalStatus value."
// The example displays the following output:
//       Converted '-1' to Late
//       Converted 'Early' to Early
Dim number As String = "-1"
Dim name As String = "Early"
Dim invalid As String = "32"
    Dim status1 As ArrivalStatus8 = CType([Enum].Parse(GetType(ArrivalStatus8), number), ArrivalStatus8)
    If Not [Enum].IsDefined(GetType(ArrivalStatus8), status1) Then status1 = ArrivalStatus8.Unknown
    Console.WriteLine("Converted '{0}' to {1}", number, status1)
Catch e As FormatException
    Console.WriteLine("Unable to convert '{0}' to an ArrivalStatus8 value.",
                   number)
End Try
Dim status2 As ArrivalStatus8
If [Enum].TryParse(Of ArrivalStatus8)(name, status2) Then
    If Not [Enum].IsDefined(GetType(ArrivalStatus8), status2) Then status2 = ArrivalStatus8.Unknown
    Console.WriteLine("Converted '{0}' to {1}", name, status2)
    Console.WriteLine("Unable to convert '{0}' to an ArrivalStatus8 value.",
                   number)
End If
' The example displays the following output:
'       Converted '-1' to Late
'       Converted 'Early' to Early
设置枚举值的格式
可以通过调用静态 Format 方法以及实例 ToString 方法的重载，将枚举值转换为其字符串表示形式。 可以使用格式字符串来控制枚举值表示为字符串的精确方式。 有关详细信息，请参阅 枚举格式字符串。 以下示例使用每个受支持的枚举格式字符串（“G”或“g”、“D”或“d”、“X”或“x”和“F”或“f”）将枚举的成员 ArrivalStatus 转换为其字符串表示形式。
string[] formats = { "G", "F", "D", "X" };
ArrivalStatus status = ArrivalStatus.Late;
foreach (var fmt in formats)
    Console.WriteLine(status.ToString(fmt));
// The example displays the following output:
//       Late
//       Late
//       -1
//       FFFFFFFF
let formats = [ "G"; "F"; "D"; "X" ]
let status = ArrivalStatus.Late
for fmt in formats do
    printfn $"{status.ToString fmt}"
// The example displays the following output:
//       Late
//       Late
//       -1
//       FFFFFFFF
Dim formats() As String = {"G", "F", "D", "X"}
Dim status As ArrivalStatus6 = ArrivalStatus6.Late
For Each fmt As String In formats
    Console.WriteLine(status.ToString(fmt))
' The example displays the following output:
'       Late
'       Late
'       -1
'       FFFFFFFF
循环访问枚举成员
该 Enum 类型不实现 IEnumerable 或 IEnumerable<T> 接口，这使你能够使用 foreach （在 C#中）、 for..in （在 F# 中）或 For Each （在 Visual Basic）构造中循环访问集合的成员。 但是，可以通过以下两种方式之一枚举成员。
可以调用 GetNames 该方法来检索包含枚举成员名称的字符串数组。 接下来，对于字符串数组的每个元素，可以调用 Parse 该方法将字符串转换为其等效的枚举值。 下面的示例阐释了这种方法。
string[] names = Enum.GetNames(typeof(ArrivalStatus));
Console.WriteLine("Members of {0}:", typeof(ArrivalStatus).Name);
Array.Sort(names);
foreach (var name in names)
    ArrivalStatus status = (ArrivalStatus)Enum.Parse(typeof(ArrivalStatus), name);
    Console.WriteLine("   {0} ({0:D})", status);
// The example displays the following output:
//       Members of ArrivalStatus:
//          Early (1)
//          Late (-1)
//          OnTime (0)
//          Unknown (-3)
let names = Enum.GetNames typeof<ArrivalStatus>
printfn $"Members of {nameof ArrivalStatus}:"
let names = Array.sort names
for name in names do
    let status = Enum.Parse(typeof<ArrivalStatus>, name) :?> ArrivalStatus
    printfn $"   {status} ({status:D})"
// The example displays the following output:
//       Members of ArrivalStatus:
//          Early (1)
//          Late (-1)
//          OnTime (0)
//          Unknown (-3)
Dim names() As String = [Enum].GetNames(GetType(ArrivalStatus7))
Console.WriteLine("Members of {0}:", GetType(ArrivalStatus7).Name)
Array.Sort(names)
For Each name In names
    Dim status As ArrivalStatus7 = CType([Enum].Parse(GetType(ArrivalStatus7), name),
                               ArrivalStatus7)
    Console.WriteLine("   {0} ({0:D})", status)
' The example displays the following output:
'       Members of ArrivalStatus7:
'          Early (1)
'          Late (-1)
'          OnTime (0)
'          Unknown (-3)
可以调用 GetValues 该方法来检索包含枚举中基础值的数组。 接下来，对于数组的每个元素，可以调用 ToObject 该方法将整数转换为其等效的枚举值。 下面的示例阐释了这种方法。
var values = Enum.GetValues(typeof(ArrivalStatus));
Console.WriteLine("Members of {0}:", typeof(ArrivalStatus).Name);
foreach (ArrivalStatus status in values)
    Console.WriteLine("   {0} ({0:D})", status);
// The example displays the following output:
//       Members of ArrivalStatus:
//          OnTime (0)
//          Early (1)
//          Unknown (-3)
//          Late (-1)
let values = Enum.GetValues typeof<ArrivalStatus>
printfn $"Members of {nameof ArrivalStatus}:"
for status in values do
    printfn $"   {status} ({status:D})"
// The example displays the following output:
//       Members of ArrivalStatus:
//          OnTime (0)
//          Early (1)
//          Unknown (-3)
//          Late (-1)
Dim values = [Enum].GetValues(GetType(ArrivalStatus7))
Console.WriteLine("Members of {0}:", GetType(ArrivalStatus7).Name)
For Each value In values
    Dim status As ArrivalStatus7 = CType([Enum].ToObject(GetType(ArrivalStatus7), value),
                                     ArrivalStatus7)
    Console.WriteLine("   {0} ({0:D})", status)
' The example displays the following output:
'       Members of ArrivalStatus7:
'          OnTime (0)
'          Early (1)
'          Unknown (-3)
'          Late (-1)
非独占成员和 Flags 属性
枚举的一个常见用途是表示一组互斥值。 例如， ArrivalStatus 实例可以有一个值 Early， OnTime或者 Late。 实例的值 ArrivalStatus 反映多个枚举常量并无意义。
但是，在其他情况下，枚举对象的值可以包含多个枚举成员，并且每个成员表示枚举值中的位字段。 该 FlagsAttribute 特性可用于指示枚举包含位字段。 例如，命名 Pets 的枚举可用于指示家庭中的宠物种类。 可以按如下方式定义它。
[Flags]
public enum Pets
    None = 0, Dog = 1, Cat = 2, Bird = 4, Rodent = 8,
    Reptile = 16, Other = 32
[<Flags>] 
type Pets =
    | None = 0
    | Dog = 1
    | Cat = 2
    | Bird = 4
    | Rodent = 8
    | Reptile = 16
    | Other = 32
<Flags> Public Enum Pets As Integer
   None = 0
   Dog = 1
   Cat = 2
   Bird = 4
   Rodent = 8
   Reptile = 16
   Other = 32
End Enum
Pets然后，可以使用枚举，如以下示例所示。
Pets familyPets = Pets.Dog | Pets.Cat;
Console.WriteLine("Pets: {0:G} ({0:D})", familyPets);
// The example displays the following output:
//       Pets: Dog, Cat (3)
let familyPets = Pets.Dog ||| Pets.Cat
printfn $"Pets: {familyPets:G} ({familyPets:D})"
// The example displays the following output:
//       Pets: Dog, Cat (3)
Dim familyPets As Pets = Pets.Dog Or Pets.Cat
Console.WriteLine("Pets: {0:G} ({0:D})", familyPets)
' The example displays the following output:
'       Pets: Dog, Cat (3)
定义按位枚举并应用 FlagsAttribute 属性时，应使用以下最佳做法。
FlagsAttribute仅当对数值执行按位运算（AND、OR、EXCLUSIVE OR）时，才对枚举使用自定义属性。
定义两个（即 1、2、4、8 等）的枚举常量。 这意味着组合枚举常量中的单个标志不会重叠。
请考虑为常用标志组合创建枚举常量。 例如，如果你有用于包含枚举常量的文件 I/O 操作的 Read = 1 枚举，请考虑 Write = 2创建枚举常量，该常量 ReadWrite = Read OR Write合并 Read 了和 Write 标志。 此外，在某些情况下，用于合并标志的按位 OR 操作可能被视为不需要简单任务的高级概念。
如果将负数定义为标志枚举常量，请使用警告，因为许多标志位置可能设置为 1，这可能会导致代码混乱，并鼓励编码错误。
测试数值中是否设置标志的简便方法是调用实例 HasFlag 方法，如以下示例所示。
Pets familyPets = Pets.Dog | Pets.Cat;
if (familyPets.HasFlag(Pets.Dog))
    Console.WriteLine("The family has a dog.");
// The example displays the following output:
//       The family has a dog.
let familyPets = Pets.Dog ||| Pets.Cat
if familyPets.HasFlag Pets.Dog then
    printfn "The family has a dog."
// The example displays the following output:
//       The family has a dog.
Dim familyPets As Pets = Pets.Dog Or Pets.Cat
If familyPets.HasFlag(Pets.Dog) Then
    Console.WriteLine("The family has a dog.")
End If
' The example displays the following output:
'       The family has a dog.
它等效于在数值和标志枚举常量之间执行按位 AND 运算，该常量将数值中的所有位设置为零，这些位与标志不对应，然后测试该操作的结果是否等于标志枚举常量。 下列示例对此进行了阐释。
Pets familyPets = Pets.Dog | Pets.Cat;
if ((familyPets & Pets.Dog) == Pets.Dog)
    Console.WriteLine("The family has a dog.");
// The example displays the following output:
//       The family has a dog.
let familyPets = Pets.Dog ||| Pets.Cat
if (familyPets &&& Pets.Dog) = Pets.Dog then
    printfn "The family has a dog."
// The example displays the following output:
//       The family has a dog.
Dim familyPets As Pets = Pets.Dog Or Pets.Cat
If familyPets And Pets.Dog = Pets.Dog Then
    Console.WriteLine("The family has a dog.")
End If
' The example displays the following output:
'       The family has a dog.
用作 None 其值为零的标志枚举常量的名称。 不能在按位 AND 操作中使用 None 枚举常量来测试标志，因为结果始终为零。 但是，可以执行数值与 None 枚举常量之间的逻辑而不是按位比较，以确定是否设置了数值中的任何位。 下列示例对此进行了阐释。
Pets familyPets = Pets.Dog | Pets.Cat;
if (familyPets == Pets.None)
    Console.WriteLine("The family has no pets.");
    Console.WriteLine("The family has pets.");
// The example displays the following output:
//       The family has pets.
let familyPets = Pets.Dog ||| Pets.Cat
if familyPets = Pets.None then
    printfn "The family has no pets."
    printfn "The family has pets."
// The example displays the following output:
//       The family has pets.
Dim familyPets As Pets = Pets.Dog Or Pets.Cat
If familyPets = Pets.None Then
    Console.WriteLine("The family has no pets.")
    Console.WriteLine("The family has pets.")
End If
' The example displays the following output:
'       The family has pets.
不要只定义枚举值以镜像枚举本身的状态。 例如，不要定义仅标记枚举末尾的枚举常量。 如果需要确定枚举的最后一个值，请显式检查该值。 此外，如果范围中的所有值有效，则可以对第一个和最后一个枚举常量执行范围检查。
添加枚举方法
由于枚举类型由语言结构（如 enum （C#）和 Enum （Visual Basic）定义，因此不能为枚举类型定义自定义方法，而不是从 Enum 类继承的那些方法。 但是，可以使用扩展方法将功能添加到特定枚举类型。
在下面的示例中，Grades 枚举表示学生可能在班里收到的字母等级分。 该示例将一个名为 Passing 的扩展方法添加到 Grades 类型中，以便该类型的每个实例现在都“知道”它是否表示合格的等级分。      该 Extensions 类还包含一个静态读/写变量，用于定义最低通过成绩。 扩展方法的 Passing 返回值反映了该变量的当前值。
using System;
// Define an enumeration to represent student grades.
public enum Grades { F = 0, D = 1, C = 2, B = 3, A = 4 };
// Define an extension method for the Grades enumeration.
public static class Extensions
    public static Grades minPassing = Grades.D;
    public static bool Passing(this Grades grade)
        return grade >= minPassing;
class Example8
    static void Main()
        Grades g1 = Grades.D;
        Grades g2 = Grades.F;
        Console.WriteLine("{0} {1} a passing grade.", g1, g1.Passing() ? "is" : "is not");
        Console.WriteLine("{0} {1} a passing grade.", g2, g2.Passing() ? "is" : "is not");
        Extensions.minPassing = Grades.C;
        Console.WriteLine("\nRaising the bar!\n");
        Console.WriteLine("{0} {1} a passing grade.", g1, g1.Passing() ? "is" : "is not");
        Console.WriteLine("{0} {1} a passing grade.", g2, g2.Passing() ? "is" : "is not");
// The exmaple displays the following output:
//       D is a passing grade.
//       F is not a passing grade.
//       Raising the bar!
//       D is not a passing grade.
//       F is not a passing grade.
open System
open System.Runtime.CompilerServices
// Define an enumeration to represent student grades.
type Grades =
    | F = 0
    | D = 1
    | C = 2
    | B = 3
    | A = 4
let mutable minPassing = Grades.D
// Define an extension method for the Grades enumeration.
[<Extension>]
type Extensions =
    [<Extension>]
    static member Passing(grade) = grade >= minPassing
let g1 = Grades.D
let g2 = Grades.F
printfn $"""{g1} {if g1.Passing() then "is" else "is not"} a passing grade."""
printfn $"""{g2} {if g2.Passing() then "is" else "is not"} a passing grade."""
minPassing <- Grades.C
printfn "\nRaising the bar!\n"
printfn $"""{g1} {if g1.Passing() then "is" else "is not"} a passing grade."""
printfn $"""{g2} {if g2.Passing() then "is" else "is not"} a passing grade."""
// The exmaple displays the following output:
//       D is a passing grade.
//       F is not a passing grade.
//       Raising the bar!
//       D is not a passing grade.
//       F is not a passing grade.
Imports System.Runtime.CompilerServices
' Define an enumeration to represent student grades.
Public Enum Grades As Integer
   F = 0
   D = 1
   C = 2
   B = 3
   A = 4
End Enum   
' Define an extension method for the Grades enumeration.
Public Module Extensions
  Public minPassing As Grades = Grades.D
  <Extension>
  Public Function Passing(grade As Grades) As Boolean
     Return grade >= minPassing
  End Function
End Module
Public Module Example
  Public Sub Main()
      Dim g1 As Grades = Grades.D
      Dim g2 As Grades = Grades.F
      Console.WriteLine("{0} {1} a passing grade.", 
                        g1, If(g1.Passing(), "is", "is not"))
      Console.WriteLine("{0} {1} a passing grade.", 
                        g2, If(g2.Passing(), "is", "is not"))
      Console.WriteLine()
      Extensions.minPassing = Grades.C
      Console.WriteLine("Raising the bar!")
      Console.WriteLine()
      Console.WriteLine("{0} {1} a passing grade.", 
                        g1, If(g1.Passing(), "is", "is not"))
      Console.WriteLine("{0} {1} a passing grade.", 
                        g2, If(g2.Passing(), "is", "is not"))
  End Sub
End Module
' The exmaple displays the following output:
'       D is a passing grade.
'       F is not a passing grade.
'       Raising the bar!
'       D is not a passing grade.
'       F is not a passing grade.
以下示例演示如何使用枚举来表示命名值，使用另一个枚举来表示命名位字段。
using System;
public class EnumTest {
    enum Days { Saturday, Sunday, Monday, Tuesday, Wednesday, Thursday, Friday };
    enum BoilingPoints { Celsius = 100, Fahrenheit = 212 };
    [Flags]
    enum Colors { Red = 1, Green = 2, Blue = 4, Yellow = 8 };
    public static void Main() {
        Type weekdays = typeof(Days);
        Type boiling = typeof(BoilingPoints);
        Console.WriteLine("The days of the week, and their corresponding values in the Days Enum are:");
        foreach ( string s in Enum.GetNames(weekdays) )
            Console.WriteLine( "{0,-11}= {1}", s, Enum.Format( weekdays, Enum.Parse(weekdays, s), "d"));
        Console.WriteLine();
        Console.WriteLine("Enums can also be created which have values that represent some meaningful amount.");
        Console.WriteLine("The BoilingPoints Enum defines the following items, and corresponding values:");
        foreach ( string s in Enum.GetNames(boiling) )
            Console.WriteLine( "{0,-11}= {1}", s, Enum.Format(boiling, Enum.Parse(boiling, s), "d"));
        Colors myColors = Colors.Red | Colors.Blue | Colors.Yellow;
        Console.WriteLine();
        Console.WriteLine("myColors holds a combination of colors. Namely: {0}", myColors);
open System
type Days =
    | Saturday = 0
    | Sunday = 1
    | Monday = 2
    | Tuesday = 3
    | Wednesday = 4
    | Thursday = 5
    | Friday = 6
type BoilingPoints =
    | Celsius = 100
    | Fahrenheit = 212
[<Flags>]
type Colors =
    | Red = 1
    | Green = 2
    | Blue = 4
    | Yellow = 8
let weekdays = typeof<Days>
let boiling = typeof<BoilingPoints>
printfn "The days of the week, and their corresponding values in the Days Enum are:"
for s in Enum.GetNames weekdays do
    printfn $"""{s,-11}= {Enum.Format(weekdays, Enum.Parse(weekdays, s), "d")}"""
printfn "\nEnums can also be created which have values that represent some meaningful amount."
printfn "The BoilingPoints Enum defines the following items, and corresponding values:"
for s in Enum.GetNames boiling do
    printfn $"""{s,-11}= {Enum.Format(boiling, Enum.Parse(boiling, s), "d")}"""
let myColors = Colors.Red ||| Colors.Blue ||| Colors.Yellow
printfn $"\nmyColors holds a combination of colors. Namely: {myColors}"
Public Class EnumTest
    Enum Days
        Saturday
        Sunday
        Monday
        Tuesday
        Wednesday
        Thursday
        Friday
    End Enum 
    Enum BoilingPoints
        Celsius = 100
        Fahrenheit = 212
    End Enum 
    <Flags()> _
    Enum Colors
        Red = 1
        Green = 2
        Blue = 4
        Yellow = 8
    End Enum 
    Public Shared Sub Main()
        Dim weekdays As Type = GetType(Days)
        Dim boiling As Type = GetType(BoilingPoints)
        Console.WriteLine("The days of the week, and their corresponding values in the Days Enum are:")
        Dim s As String
        For Each s In  [Enum].GetNames(weekdays)
            Console.WriteLine("{0,-11} = {1}", s, [Enum].Format(weekdays, [Enum].Parse(weekdays, s), "d"))
        Next s
        Console.WriteLine()
        Console.WriteLine("Enums can also be created which have values that represent some meaningful amount.")
        Console.WriteLine("The BoilingPoints Enum defines the following items, and corresponding values:")
        For Each s In  [Enum].GetNames(boiling)
            Console.WriteLine("{0,-11} = {1}", s, [Enum].Format(boiling, [Enum].Parse(boiling, s), "d"))
        Next s
        Dim myColors As Colors = Colors.Red Or Colors.Blue Or Colors.Yellow
        Console.WriteLine()
        Console.WriteLine("myColors holds a combination of colors. Namely: {0}", myColors)
    End Sub 
End Class