设计模式中枚举的替代方案

Question

考虑基本程序集base 具有类似enum 类型的情况

public enum ItemState = { red, green, blue };

我在其他程序集Project_1、Project_2 等中使用此基础程序集。

他们每个人都做一些特定的事情，并且需要特定于项目的状态，例如Project_1 中的{grey, black, white, ...} 和Project_2 中的{brown, transparent, ...}。

Project_1 不允许使用（如果可能的话，甚至可以看到）{brown, transparent, ...}。同样，Project_2 不能使用{grey, black, white, ...}。

我知道“部分枚举”不存在 - 那么此类任务的建议设计模式是什么？

Answer 1

根据您的用例，您可能希望使用主/子集模式。

例如，我有一个包含所有可能值的枚举：

/// <summary>
/// Types of limits that can be applied to a table, view, or table-value function query.
/// </summary>
/// <remarks>Databases are expected to provide their own enumeration that represents a subset of these options.</remarks>
[Flags]
public enum LimitOptions
{
    /// <summary>
    /// No limits were applied.
    /// </summary>
    None = 0,

    /// <summary>
    /// Returns the indicated number of rows with optional offset
    /// </summary>
    Rows = 1,

    /// <summary>
    /// Returns the indicated percentage of rows. May be applied to TableSample
    /// </summary>
    Percentage = 2,


    /// <summary>
    /// Adds WithTies behavior to Rows or Percentage
    /// </summary>
    WithTies = 4,


    /// <summary>
    /// Returns the top N rows. When there is a tie for the Nth record, this will cause it to be returned. 
    /// </summary>
    RowsWithTies = Rows | WithTies,

    /// <summary>
    /// Returns the top N rpercentage of ows. When there is a tie for the Nth record, this will cause it to be returned. 
    /// </summary>
    PercentageWithTies = Percentage | WithTies,

那么每个项目都有自己的价值子集：

/// <summary>
/// Limit options supported by Access.
/// </summary>
/// <remarks>This is a strict subset of LimitOptions</remarks>
public enum AccessLimitOption
{
    /// <summary>
    /// No limits were applied.
    /// </summary>
    None = LimitOptions.None,

    /// <summary>
    /// Uses TOP
    /// </summary>
    RowsWithTies = LimitOptions.RowsWithTies,

}

子项目始终使用严格的子集，而不是使枚举可扩展。这使我能够保持核心相当通用，同时在适当的情况下提供特定于数据库的 API。

Answer 2

我有点晚了，但这里是 Rene 答案的“抛光”版本（现在带有隐式转换！）：

public class ColorEnum
{
    protected readonly string Name;
    protected readonly Color Value;

    public static readonly ColorEnum Red = new ColorEnum(Color.Red, "Red");
    public static readonly ColorEnum Green = new ColorEnum(Color.Green, "Green");
    public static readonly ColorEnum Blue = new ColorEnum(Color.Blue, "Blue");

    protected ColorEnum(Color value, string name)
    {
        Name = name;
        Value = value;
    }

    public override string ToString()
    {
        return Name;
    }

    public static implicit operator Color(ColorEnum @enum)
    {
        return @enum.Value;
    }

    public static implicit operator string(ColorEnum @enum)
    {
        return @enum.Name;
    }
}

public class AnotherColorEnum : ColorEnum
{
    public static readonly ColorEnum Grey = new AnotherColorEnum(Color.Gray, "Grey");
    public static readonly ColorEnum Black = new AnotherColorEnum(Color.Black, "Black");
    public static readonly ColorEnum White = new AnotherColorEnum(Color.White, "White");

    protected AnotherColorEnum(Color value, string name) : base(value, name)
    {
    }
}

这样你就可以像这样使用你的“枚举”：

    var color = ColorEnum.Red;
    var anothercolor = Color.Red;
    if (color == anothercolor)
    {
            //DoSomething
    }

或者像这样：

    var color = ColorEnum.Red;
    var anothercolor = "Red";
    if (color == anothercolor)
    {
            //DoSomething
    }

Answer 3

由于无法继承枚举，一种解决方案可能是使用具有静态常量成员的类，如下所示：

public class ItemState
{
    protected ItemState() { }

    public static ItemState red { get; } = new ItemState();
    public static ItemState green { get; } = new ItemState();
    public static ItemState blue { get; } = new ItemState();
}

然后在你的Project_1 中你可以派生一个自己的类：

public class ItemState_1 : ItemState
{
    public static ItemState grey { get; } = new ItemState_1();
    public static ItemState black white { get; } = new ItemState_1();
}

在Project_2

public class ItemState_2 : ItemState
{
    public static ItemState brown { get; } = new ItemState_2();
    public static ItemState transparent white { get; } = new ItemState_2();
}

这可能不是最舒服的方式，但我现在能想到的最好的方式。

你可以这样使用它们：

ItemState project1State = ItemState_1.grey;

if (project1State == ItemState_1.grey)
   // do something

这一切都编译得很好，但不幸的是这些值不能在switch/case 语句中使用。这可以通过正确的ToString() 实现来解决，字符串文字可以在switch/case 中使用。但这当然会为这些类/属性定义添加更多代码。