C#でenumは継承できない？代替案と列挙型を共通化する設計手法を解説

using System;
using System.Collections.Generic;
using System.Linq;

// 基底となる列挙型クラス
public abstract class ErrorCode
{
    public string Name { get; }
    public int Value { get; }

    protected ErrorCode(string name, int value)
    {
        Name = name;
        Value = value;
    }

    // 共通の静的値
    public static readonly ErrorCode Success = new BaseErrorCode("Success", 0);
    public static readonly ErrorCode Unknown = new BaseErrorCode("Unknown", -1);

    // 内部用の具象クラス
    private class BaseErrorCode : ErrorCode
    {
        public BaseErrorCode(string name, int value) : base(name, value) { }
    }

    public override string ToString() => $"{Name} ({Value})";
}

// 継承した特定のドメイン用エラーコード
public class NetworkErrorCode : ErrorCode
{
    protected NetworkErrorCode(string name, int value) : base(name, value) { }

    public static readonly NetworkErrorCode Timeout = new NetworkErrorCode("Timeout", 1001);
    public static readonly NetworkErrorCode ConnectionLost = new NetworkErrorCode("ConnectionLost", 1002);
}

public class Program
{
    public static void Main()
    {
        // 基底クラスの値と派生クラスの値を同様に扱える
        Console.WriteLine($"Status: {ErrorCode.Success}");
        Console.WriteLine($"Status: {NetworkErrorCode.Timeout}");
    }
}

public enum OrderStatus
{
    Pending,
    Processing,
    Shipped,
    Cancelled
}

public static class OrderStatusExtensions
{
    // 列挙型に表示名を取得するメソッドを追加
    public static string ToDisplayName(this OrderStatus status)
    {
        return status switch
        {
            OrderStatus.Pending => "保留中",
            OrderStatus.Processing => "処理中",
            OrderStatus.Shipped => "出荷済み",
            OrderStatus.Cancelled => "キャンセル",
            _ => "不明"
        };
    }

    // 特定の条件判定ロジックを共通化
    public static bool IsFinalState(this OrderStatus status)
    {
        return status == OrderStatus.Shipped || status == OrderStatus.Cancelled;
    }
}

class Program
{
    static void Main()
    {
        OrderStatus current = OrderStatus.Shipped;
        
        // あたかもenumがメソッドを持っているかのように呼び出せる
        Console.WriteLine($"現在のステータス: {current.ToDisplayName()}");
        Console.WriteLine($"完了状態か: {current.IsFinalState()}");
    }
}

using System;

public class EnumHelper
{
    // Enum制約を利用した汎用メソッド
    public static void PrintEnumDetails<T>(T enumValue) where T : struct, Enum
    {
        string name = Enum.GetName(typeof(T), enumValue);
        int value = Convert.ToInt32(enumValue);
        
        Console.WriteLine($"Type: {typeof(T).Name}, Name: {name}, Value: {value}");
    }
}

public enum UserRole { Admin, Editor, Viewer }
public enum LogLevel { Info, Warning, Error }

class Program
{
    static void Main()
    {
        EnumHelper.PrintEnumDetails(UserRole.Admin);
        EnumHelper.PrintEnumDetails(LogLevel.Error);
    }
}

public struct AppConstants
{
    public struct UI
    {
        public const string PrimaryColor = "#FF0000";
        public const int DefaultPadding = 16;
    }

    public struct API
    {
        public const string BaseUrl = "https://api.example.com";
        public const int TimeoutSeconds = 30;
    }
}