在C＃中，如何像enum一樣使用struct？

Question

我有一個結構，我試圖像枚舉一樣使用：

public struct SQLDS_statementTypes
{
    public static string Select = "Select", 
        Update = "Update", Insert = "Insert", Delete = "Delete";
}

但它拋出一個錯誤： “運算符'=='不能應用於此語句中'SQLDS_statementTypes'和'string'類型的操作數 ：

if (statement == SQLDS_statementTypes.Update)

反正有沒有解決這個問題？

Answer 1

為什么不使用常規枚舉？ http://msdn.microsoft.com/en-us/library/sbbt4032.aspx

Answer 2

有人在尋找一些看起來或多或少你正在尋找的東西（我找不到鏈接的麻煩）我當時就寫了這個。 您可能希望將類名更改為更符合您的需要。 我希望添加/刪除值的配置很簡單，如果沒有我可以詳細說明。

public struct Group
{
    #region Code that is to be configured
    public static readonly Group Alpha = new Group("Group Alpha");
    public static readonly Group Beta = new Group("Group Beta");
    public static readonly Group Invalid = new Group("N/A");


    public static IEnumerable<Group> AllGroups
    {
        get
        {
            yield return Alpha;
            yield return Beta;
            yield return Invalid;
            //...
            //add a yield return for all instances here.
        }
    }

    #endregion
    private string value;

    /// <summary>
    /// default constructor
    /// </summary>
    //private Group()
    //{
    //    //you can make this default value whatever you want.  null is another option I considered, but you 
    //    //shouldn't have this me anything that doesn't exist as one of the options defined at the top of 
    //    //the page.
    //    value = "N/A";
    //}
    /// <summary>
    /// primary constructor
    /// </summary>
    /// <param name="value">The string value that this is a wrapper for</param>
    private Group(string value)
    {
        this.value = value;
    }

    /// <summary>
    /// Compares the Group to another group, or to a string value.
    /// </summary>
    /// <param name="obj"></param>
    /// <returns></returns>
    public override bool Equals(object obj)
    {
        if (obj is Group)
        {
            return this.value.Equals(((Group)obj).value);
        }

        string otherString = obj as string;
        if (otherString != null)
        {
            return this.value.Equals(otherString);
        }

        throw new ArgumentException("obj is neither a Group nor a String");
    }

    public override int GetHashCode()
    {
        return value.GetHashCode();
    }

    /// <summary>
    /// returns the internal string that this is a wrapper for.
    /// </summary>
    /// <param name="group"></param>
    /// <returns></returns>
    public static implicit operator string(Group group)
    {
        return group.value;
    }

    /// <summary>
    /// Parses a string and returns an instance that corresponds to it.
    /// </summary>
    /// <param name="input"></param>
    /// <returns></returns>
    public static Group Parse(string input)
    {
        return AllGroups.Where(item => item.value == input).FirstOrDefault();
    }

    /// <summary>
    /// Syntatic sugar for the Parse method.
    /// </summary>
    /// <param name="other"></param>
    /// <returns></returns>
    public static explicit operator Group(string other)
    {
        return Parse(other);
    }

    public override string ToString()
    {
        return value;
    }
}

Answer 3

你不能。 如果你想進行這樣的字符串比較，為什么不使用公共成員的靜態類呢？

static class StatementTypes
{
    public static Select
    {
        get { return "Select"; }
    }
}

然后你可以在比較中使用StatementTypes.Select。

Answer 4

錯誤是正確的，我認為（來自錯誤）該statement的類型為SQLDS_statementTypes，但SQLDS_statementTypes.Update的類型為string ，因此您嘗試將結構與字符串進行比較，默認情況下對C＃沒有意義。

創建類型string statement ，如果你真的想這樣做它會編譯，雖然我不知道你為什么不首先使用常規enum 。

您是否嘗試獲取枚舉的string值？ C＃默認情況下已經這樣做了：

public enum Coordinates
{
    Cartesian,
    Polar
}

...

// x will contain the string "Cartesian"
var x = Coordinates.Cartesian.ToString();