C# 在C中使用枚举作为数组索引#

我想做与中相同的事情，即：

enum DaysOfTheWeek {Sunday=0, Monday, Tuesday...};
string[] message_array = new string[number_of_items_at_enum];

...

Console.Write(custom_array[(int)DaysOfTheWeek.Sunday]);

---

然而，我更希望有一些集成的东西，而不是编写这种容易出错的代码。C#中是否有一个内置模块可以做到这一点？

如果枚举项的值是连续的，那么数组方法工作得很好。但是，在任何情况下，您都可以使用

字典
（顺便说一句，它的性能较差）。
您可以创建一个类或结构来完成这项工作


编辑

由于没有更好的地方来表达这一点，我在下面发布了一个Caster类的通用版本。不幸的是，它依赖于运行时检查来将TKey强制作为枚举

public enum DayOfWeek
{
    Weekend,
    Sunday = 0,
    Monday,
    Tuesday,
    Wednesday,
    Thursday,
    Friday,
    Saturday
}

public class TypeNotSupportedException : ApplicationException
{
    public TypeNotSupportedException(Type type)
        : base(string.Format("The type \"{0}\" is not supported in this context.", type.Name))
    {
    }
}

public class CannotBeIndexerException : ApplicationException
{
    public CannotBeIndexerException(Type enumUnderlyingType, Type indexerType)
        : base(
            string.Format("The base type of the enum (\"{0}\") cannot be safely cast to \"{1}\".",
                          enumUnderlyingType.Name, indexerType)
            )
    {
    }
}

public class Caster<TKey, TValue>
{
    private readonly Type baseEnumType;

    public Caster()
    {
        baseEnumType = typeof(TKey);
        if (!baseEnumType.IsEnum)
            throw new TypeNotSupportedException(baseEnumType);
    }

    public Caster(TValue[] data)
        : this()
    {
        Data = data;
    }

    public TValue this[TKey key]
    {
        get
        {
            var enumUnderlyingType = Enum.GetUnderlyingType(baseEnumType);
            var intType = typeof(int);
            if (!enumUnderlyingType.IsAssignableFrom(intType))
                throw new CannotBeIndexerException(enumUnderlyingType, intType);
            var index = (int) Enum.Parse(baseEnumType, key.ToString());
            return Data[index];
        }
    }

    public TValue[] Data { get; set; }


    public static implicit operator TValue[](Caster<TKey, TValue> caster)
    {
        return caster.Data;
    }

    public static implicit operator Caster<TKey, TValue>(TValue[] data)
    {
        return new Caster<TKey, TValue>(data);
    }
}

// declaring and using it.
Caster<DayOfWeek, string> messageArray =
    new[]
        {
            "Sunday",
            "Monday",
            "Tuesday",
            "Wednesday",
            "Thursday",
            "Friday",
            "Saturday"
        };
Console.WriteLine(messageArray[DayOfWeek.Sunday]);
Console.WriteLine(messageArray[DayOfWeek.Monday]);
Console.WriteLine(messageArray[DayOfWeek.Tuesday]);
Console.WriteLine(messageArray[DayOfWeek.Wednesday]);
Console.WriteLine(messageArray[DayOfWeek.Thursday]);
Console.WriteLine(messageArray[DayOfWeek.Friday]);
Console.WriteLine(messageArray[DayOfWeek.Saturday]);

public enum DayOfWeek
{
周末,，
星期日=0，
星期一，
星期二，
星期三，
星期四，
星期五，
星期六
}
公共类TypeNotSupportedException:ApplicationException
{
公共类型不支持异常（类型类型）
：base（string.Format（“此上下文中不支持类型\“{0}\”，type.Name））
{
}
}
公共类不能索引Exception:ApplicationException
{
公共CannotBeIndexerException（类型EnumUnderlineType，类型indexerType）
：基本(
Format（“枚举的基类型（\“{0}\”）不能安全地强制转换为\“{1}\”，
EnumUnderlineType.Name，indexerType）
)
{
}
}
公共级连铸机
{
私有只读类型baseEnumType；
公共播音员（）
{
baseEnumType=typeof（TKey）；
如果（！baseEnumType.IsEnum）
抛出新类型NotSupportedException（baseEnumType）；
}
公共广播（TValue[]数据）
：此（）
{
数据=数据；
}
公共TValue此[TKey]
{
得到
{
var enumUnderlyngType=Enum.GetUnderlyngType（baseEnumType）；
var intType=typeof（int）；
如果（！EnumUnderlineType.IsAssignableFrom（intType））
抛出新的CannotBeIndexerException（EnumUnderlineType，intType）；
var index=（int）Enum.Parse（baseEnumType，key.ToString（））；
返回数据[索引]；
}
}
公共TValue[]数据{get；set；}
公共静态隐式运算符TValue[]（Caster-Caster）
{
返回主销数据；
}
公共静态隐式运算符Caster（TValue[]数据）
{
返回新的主销后倾角（数据）；
}
}
//声明和使用它。
Caster消息数组=
新[]
{
“星期日”，
“星期一”，
“星期二”，
“星期三”，
“星期四”，
“星期五”，
“星期六”
};
WriteLine（messageArray[DayOfWeek.Sunday]）；
WriteLine（messageArray[DayOfWeek.Monday]）；
WriteLine（messageArray[DayOfWeek.周二]）；
WriteLine（messageArray[DayOfWeek.周三]）；
WriteLine（messageArray[DayOfWeek.周四]）；
WriteLine（messageArray[DayOfWeek.Friday]）；
WriteLine（messageArray[DayOfWeek.Saturday]）；
给你：

string[] message_array = Enum.GetNames(typeof(DaysOfTheWeek));

如果您确实需要长度，那么只需在结果上选择.length:）
您可以通过以下方式获取值：

string[] message_array = Enum.GetValues(typeof(DaysOfTheWeek));

始终可以执行一些额外的映射，以一致和定义的方式获取枚举值的数组索引：

int ArrayIndexFromDaysOfTheWeekEnum(DaysOfWeek day)
{
   switch (day)
   {
     case DaysOfWeek.Sunday: return 0;
     case DaysOfWeek.Monday: return 1;
     ...
     default: throw ...;
   }
}

尽可能具体。有一天，有人会修改您的枚举，代码将失败，因为该枚举的值被（错误地）用作数组索引。
压缩形式的枚举用作索引并将任何类型分配给字典
而且是强类型的。在这种情况下，将返回浮点值，但值可能是具有属性和方法等的复杂类实例：

enum opacityLevel { Min, Default, Max }
private static readonly Dictionary<opacityLevel, float> _oLevels = new Dictionary<opacityLevel, float>
{
    { opacityLevel.Max, 40.0 },
    { opacityLevel.Default, 50.0 },
    { opacityLevel.Min, 100.0 }
};

//Access float value like this
var x = _oLevels[opacitylevel.Default];

enum opacityLevel{Min，默认值，Max}
私有静态只读词典_oLevels=新词典
{
{opacityLevel.Max，40.0}，
{opacityLevel.Default，50.0}，
{opacityLevel.Min，100.0}
};
//像这样访问浮点值
var x=_oLevels[opacitylevel.Default]；
如果您只需要一个映射，但又不想产生与字典查找相关的性能开销，那么这可能会起作用：

    public class EnumIndexedArray<TKey, T> : IEnumerable<KeyValuePair<TKey, T>> where TKey : struct
    {
        public EnumIndexedArray()
        {
            if (!typeof (TKey).IsEnum) throw new InvalidOperationException("Generic type argument is not an Enum");
            var size = Convert.ToInt32(Keys.Max()) + 1;
            Values = new T[size];
        }

        protected T[] Values;

        public static IEnumerable<TKey> Keys
        {
            get { return Enum.GetValues(typeof (TKey)).OfType<TKey>(); }
        }

        public T this[TKey index]
        {
            get { return Values[Convert.ToInt32(index)]; }
            set { Values[Convert.ToInt32(index)] = value; }
        }

        private IEnumerable<KeyValuePair<TKey, T>> CreateEnumerable()
        {
            return Keys.Select(key => new KeyValuePair<TKey, T>(key, Values[Convert.ToInt32(key)]));
        }

        public IEnumerator<KeyValuePair<TKey, T>> GetEnumerator()
        {
            return CreateEnumerable().GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }
    }

显然，此实现由数组支持，因此非连续枚举如下：

enum
{
  Ok = 1,
  NotOk = 1000000
}

将导致内存过度使用

如果您需要尽可能高的性能，您可能希望使其不那么通用，并释放我为使其编译和工作而必须使用的所有通用枚举处理代码。但我并没有对此进行基准测试，所以也许这没什么大不了的

缓存Keys静态属性也可能有帮助。
为便于将来参考，上述问题可总结如下：

我来自Delphi，在Delphi中可以定义如下数组：

type
  {$SCOPEDENUMS ON}
  TDaysOfTheWeek = (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday);

  TDaysOfTheWeekStrings = array[TDaysOfTheWeek];

然后可以使用最小值和最大值迭代数组：

for Dow := Min(TDaysOfTheWeek) to Max(TDaysOfTheWeek) 
  DaysOfTheWeekStrings[Dow] := '';

虽然这是一个精心设计的示例，但当您稍后在代码中处理数组位置时，我可以键入
DaysOfTheWeekStrings[TDaysOfTheWeek.Monday]
。这样做的好处是，我应该增加
TDaysOfTheWeek
的大小，这样我就不必记住数组的新大小等。。。。。然而，回到C#世界。我发现了这个例子
 我意识到这是一个老问题，但有很多人评论说，到目前为止，所有解决方案都有运行时检查，以确保数据类型是枚举。下面是一个完整的解决方案（带有一些示例），其中包含编译时检查（以及我的开发伙伴的一些评论和讨论）

//没有将泛型类参数约束到枚举的好方法。下面的hack在编译时确实有效，
//虽然它很复杂。有关如何使用EnumIndexedArray和ObjEnumIndexedArray这两个类的示例，
//请参见下面的AssetClassArray。或者，例如。
//EConstraint.EnumIndexedArray x=新的EConstraint.EnumIndexedArray（）；
//看到这个帖子了吗
//      http://stackoverflow.com/questions/79126/create-generic-method-constraining-t-to-an-enum/29581813#29581813
//朱莉的回答/评论
enum
{
  Ok = 1,
  NotOk = 1000000
}

type
  {$SCOPEDENUMS ON}
  TDaysOfTheWeek = (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday);

  TDaysOfTheWeekStrings = array[TDaysOfTheWeek];

for Dow := Min(TDaysOfTheWeek) to Max(TDaysOfTheWeek) 
  DaysOfTheWeekStrings[Dow] := '';

//There is no good way to constrain a generic class parameter to an Enum.  The hack below does work at compile time,
//  though it is convoluted.  For examples of how to use the two classes EnumIndexedArray and ObjEnumIndexedArray,
//  see AssetClassArray below.  Or, e.g.
//      EConstraint.EnumIndexedArray<int, YourEnum> x = new EConstraint.EnumIndexedArray<int, YourEnum>();
//  See this post 
//      http://stackoverflow.com/questions/79126/create-generic-method-constraining-t-to-an-enum/29581813#29581813
// and the answer/comments by Julien Lebosquain
public class EConstraint : HackForCompileTimeConstraintOfTEnumToAnEnum<System.Enum> { }//THIS MUST BE THE ONLY IMPLEMENTATION OF THE ABSTRACT HackForCompileTimeConstraintOfTEnumToAnEnum
public abstract class HackForCompileTimeConstraintOfTEnumToAnEnum<SystemEnum> where SystemEnum : class
{
    //For object types T, users should use EnumIndexedObjectArray below.
    public class EnumIndexedArray<T, TEnum>
        where TEnum : struct, SystemEnum
    {
        //Needs to be public so that we can easily do things like intIndexedArray.data.sum()
        //   - just not worth writing up all the equivalent methods, and we can't inherit from T[] and guarantee proper initialization.
        //Also, note that we cannot use Length here for initialization, even if Length were defined the same as GetNumEnums up to
        //  static qualification, because we cannot use a non-static for initialization here.
        //  Since we want Length to be non-static, in keeping with other definitions of the Length property, we define the separate static
        //  GetNumEnums, and then define the non-static Length in terms of the actual size of the data array, just for clarity,
        //  safety and certainty (in case someone does something stupid like resizing data).
        public T[] data = new T[GetNumEnums()];

        //First, a couple of statics allowing easy use of the enums themselves.
        public static TEnum[] GetEnums()
        {
            return (TEnum[])Enum.GetValues(typeof(TEnum));
        }
        public TEnum[] getEnums()
        {
            return GetEnums();
        }
        //Provide a static method of getting the number of enums.  The Length property also returns this, but it is not static and cannot be use in many circumstances.
        public static int GetNumEnums()
        {
            return GetEnums().Length;
        }
        //This should always return the same as GetNumEnums, but is not static and does it in a way that guarantees consistency with the member array.
        public int Length { get { return data.Length; } }
        //public int Count  { get { return data.Length; } }

        public EnumIndexedArray() { }

        // [WDS 2015-04-17] Remove. This can be dangerous. Just force people to use EnumIndexedArray(T[] inputArray).
        // [DIM 2015-04-18] Actually, if you think about it, EnumIndexedArray(T[] inputArray) is just as dangerous:
        //   For value types, both are fine.  For object types, the latter causes each object in the input array to be referenced twice,
        //   while the former causes the single object t to be multiply referenced.  Two references to each of many is no less dangerous
        //   than 3 or more references to one. So all of these are dangerous for object types.
        //   We could remove all these ctors from this base class, and create a separate
        //         EnumIndexedValueArray<T, TEnum> : EnumIndexedArray<T, TEnum> where T: struct ...
        //   but then specializing to TEnum = AssetClass would have to be done twice below, once for value types and once
        //   for object types, with a repetition of all the property definitions.  Violating the DRY principle that much
        //   just to protect against stupid usage, clearly documented as dangerous, is not worth it IMHO.
        public EnumIndexedArray(T t)
        {
            int i = Length;
            while (--i >= 0)
            {
                this[i] = t;
            }
        }
        public EnumIndexedArray(T[] inputArray)
        {
            if (inputArray.Length > Length)
            {
                throw new Exception(string.Format("Length of enum-indexed array ({0}) to big. Can't be more than {1}.", inputArray.Length, Length));
            }
            Array.Copy(inputArray, data, inputArray.Length);
        }
        public EnumIndexedArray(EnumIndexedArray<T, TEnum> inputArray)
        {
            Array.Copy(inputArray.data, data, data.Length);
        }

        //Clean data access
        public T this[int ac] { get { return data[ac]; } set { data[ac] = value; } }
        public T this[TEnum ac] { get { return data[Convert.ToInt32(ac)]; } set { data[Convert.ToInt32(ac)] = value; } }
    }


    public class EnumIndexedObjectArray<T, TEnum> : EnumIndexedArray<T, TEnum>
        where TEnum : struct, SystemEnum
        where T : new()
    {
        public EnumIndexedObjectArray(bool doInitializeWithNewObjects = true)
        {
            if (doInitializeWithNewObjects)
            {
                for (int i = Length; i > 0; this[--i] = new T()) ;
            }
        }
        // The other ctor's are dangerous for object arrays
    }

    public class EnumIndexedArrayComparator<T, TEnum> : EqualityComparer<EnumIndexedArray<T, TEnum>>
        where TEnum : struct, SystemEnum
    {
        private readonly EqualityComparer<T> elementComparer = EqualityComparer<T>.Default;

        public override bool Equals(EnumIndexedArray<T, TEnum> lhs, EnumIndexedArray<T, TEnum> rhs)
        {
            if (lhs == rhs)
                return true;
            if (lhs == null || rhs == null)
                return false;

            //These cases should not be possible because of the way these classes are constructed.
            // HOWEVER, the data member is public, so somebody _could_ do something stupid and make 
            // data=null, or make lhs.data == rhs.data, even though lhs!=rhs (above check)
            //On the other hand, these are just optimizations, so it won't be an issue if we reomve them anyway,
            // Unless someone does something really dumb like setting .data to null or resizing to an incorrect size,
            // in which case things will crash, but any developer who does this deserves to have it crash painfully...
            //if (lhs.data == rhs.data)
            //    return true;
            //if (lhs.data == null || rhs.data == null)
            //    return false;

            int i = lhs.Length;
            //if (rhs.Length != i)
            //    return false;
            while (--i >= 0)
            {
                if (!elementComparer.Equals(lhs[i], rhs[i]))
                    return false;
            }
            return true;
        }
        public override int GetHashCode(EnumIndexedArray<T, TEnum> enumIndexedArray)
        {
            //This doesn't work: for two arrays ar1 and ar2, ar1.GetHashCode() != ar2.GetHashCode() even when ar1[i]==ar2[i] for all i (unless of course they are the exact same array object)
            //return engineArray.GetHashCode();
            //Code taken from comment by Jon Skeet - of course - in http://stackoverflow.com/questions/7244699/gethashcode-on-byte-array
            //31 and 17 are used commonly elsewhere, but maybe because everyone is using Skeet's post.
            //On the other hand, this is really not very critical.
            unchecked
            {
                int hash = 17;
                int i = enumIndexedArray.Length;
                while (--i >= 0)
                {
                    hash = hash * 31 + elementComparer.GetHashCode(enumIndexedArray[i]);
                }
                return hash;
            }
        }
    }
}

//Because of the above hack, this fails at compile time - as it should.  It would, otherwise, only fail at run time.
//public class ThisShouldNotCompile : EConstraint.EnumIndexedArray<int, bool>
//{
//}

//An example
public enum AssetClass { Ir, FxFwd, Cm, Eq, FxOpt, Cr };
public class AssetClassArrayComparator<T> : EConstraint.EnumIndexedArrayComparator<T, AssetClass> { }
public class AssetClassIndexedArray<T> : EConstraint.EnumIndexedArray<T, AssetClass>
{
    public AssetClassIndexedArray()
    {
    }
    public AssetClassIndexedArray(T t) : base(t)
    {
    }
    public AssetClassIndexedArray(T[] inputArray) :  base(inputArray)
    {
    }
    public AssetClassIndexedArray(EConstraint.EnumIndexedArray<T, AssetClass> inputArray) : base(inputArray)
    {
    }

    public T Cm    { get { return this[AssetClass.Cm   ]; } set { this[AssetClass.Cm   ] = value; } }
    public T FxFwd { get { return this[AssetClass.FxFwd]; } set { this[AssetClass.FxFwd] = value; } }
    public T Ir    { get { return this[AssetClass.Ir   ]; } set { this[AssetClass.Ir   ] = value; } }
    public T Eq    { get { return this[AssetClass.Eq   ]; } set { this[AssetClass.Eq   ] = value; } }
    public T FxOpt { get { return this[AssetClass.FxOpt]; } set { this[AssetClass.FxOpt] = value; } }
    public T Cr    { get { return this[AssetClass.Cr   ]; } set { this[AssetClass.Cr   ] = value; } }
}

//Inherit from AssetClassArray<T>, not EnumIndexedObjectArray<T, AssetClass>, so we get the benefit of the public access getters and setters above
public class AssetClassIndexedObjectArray<T> : AssetClassIndexedArray<T> where T : new()
{
    public AssetClassIndexedObjectArray(bool bInitializeWithNewObjects = true)
    {
        if (bInitializeWithNewObjects)
        {
            for (int i = Length; i > 0; this[--i] = new T()) ;
        }
    }
}

/// <summary>An array indexed by an Enum</summary>
/// <typeparam name="T">Type stored in array</typeparam>
/// <typeparam name="U">Indexer Enum type</typeparam>
public class ArrayByEnum<T,U> : IEnumerable where U : Enum // requires C# 7.3 or later
{
  private readonly T[] _array;
  private readonly int _lower;

  public ArrayByEnum()
  {
    _lower = Convert.ToInt32(Enum.GetValues(typeof(U)).Cast<U>().Min());
    int upper = Convert.ToInt32(Enum.GetValues(typeof(U)).Cast<U>().Max());
    _array = new T[1 + upper - _lower];
  }

  public T this[U key]
  {
    get { return _array[Convert.ToInt32(key) - _lower]; }
    set { _array[Convert.ToInt32(key) - _lower] = value; }
  }

  public IEnumerator GetEnumerator()
  {
    return Enum.GetValues(typeof(U)).Cast<U>().Select(i => this[i]).GetEnumerator();
  }
}

ArrayByEnum<string,MyEnum> myArray = new ArrayByEnum<string,MyEnum>();
myArray[MyEnum.First] = "Hello";

myArray[YourEnum.Other] = "World"; // compiler error