convert an enum to another type of enum

Question

I have an enum of for example  Gender   Male  0   Female  1  and I have another enum from a service which has its own Gender enum  Male  0   Female  1  Unknown  2    My question is how can I write something quick and nice to convert from their enum to mine

User · Answer

You can use ToString   to convert the first enum to its name  and then Enum Parse   to convert the string back to the other Enum  This will throw an exception if the value is not supported by the destination enum  i e  for an  Unknown  value

User · Answer

Just cast one to int and then cast it to the other enum  considering that you want the mapping done based on value    Gender2 gender2    Gender2   int gender1

User · Answer

I wrote this answer because I believe there are fundamental issues with the majority of answers already provided  and the ones that are acceptable are incomplete  Mapping by enum integer value This approach is bad simply because it assumes that the integer values of both MyGender and TheirGender will always remain comparable  In practice  it is very rare that you can guarantee this even within a single project  let alone a separate service  The approach we take should be something that can be used for other enum-mapping cases  We should never assume that one enum identically relates to another - especially when we may not have control over one or another  Mapping by enum string value This is a little better  as MyGender Male will still convert to TheirGender Male even if the integer representation is changed  but still not ideal  I would discourage this approach as it assumes the name values will not change  and will always remain identical  Considering future enhancements  you cannot guarantee that this will be the case  consider if MyGender NotKnown was added  It is likely that you would want this to map to TheirGender Unknown  but this would not be supported  Also  it is generally bad to assume that one enum equates to another by name  as this might not be the case in some contexts  As mentioned earlier  an ideal approach would work for other enum-mapping requirements  Explicitly mapping enums This approach explictly maps MyGender to TheirGender using a switch statement  This is better as   Covers the case where the underlying integer value changes  Covers the case where the enum names changes  i e  no assumptions - the developer will need to update the code to handle the scenario  - good   Handles cases where enum values cannot be mapped  Handles cases where new enum values are added and cannot be mapped by default  again  no assumptions made - good   Can easily be updated to support new enum values for either MyGender or TheirGender  The same approach can be taken for all enum mapping requirements   Assuming we have the following enums  public enum MyGender       Male   0      Female   1     public enum TheirGender       Male   0      Female   1      Unknown   2     We can create the following function to  quot convert from their enum to mine quot   public MyGender GetMyGender TheirGender theirGender        switch  theirGender                case TheirGender Male              return MyGender Male           case TheirGender Female              return MyGender Female           default              throw new InvalidEnumArgumentException nameof theirGender    int theirGender  typeof TheirGender             A previous answer suggested returning a nullable enum  TheirGender   and returning null for any unmatched input  This is bad  null is not the same as an unknown mapping  If the input cannot be mapped  an exception should be thrown  else the method should be named more explictly to the behaviour  public TheirGender  GetTheirGenderOrDefault MyGender myGender        switch  myGender                case MyGender Male              return TheirGender Male                       case MyGender Female              return TheirGender Female                       default              return default TheirGender             Additional considerations If it is likely that this method will be required more than once in various parts of the solution  you could consider creating an extension method for this  public static class TheirGenderExtensions       public static MyGender GetMyGender this TheirGender theirGender                switch  theirGender                        case TheirGender Male                  return MyGender Male               case TheirGender Female                  return MyGender Female               default                  throw new InvalidEnumArgumentException nameof theirGender    int theirGender  typeof TheirGender                       If you are using C 8  you can use the syntax for switch expressions and expression bodies to neaten up the code  public static class TheirGenderExtensions       public static MyGender GetMyGender this TheirGender theirGender            gt  theirGender switch                       TheirGender Male   gt  MyGender Male              TheirGender Female   gt  MyGender Female                  gt  throw new InvalidEnumArgumentException nameof theirGender    int theirGender  typeof TheirGender                 If you will only ever be mapping the enums within a single class  then an extension method may be overkill  In this case  the method can be declared within the class itself  Furthermore  if the mapping will only ever take place within a single method  then you can declare this as a local function  public static void Main         Console WriteLine GetMyGender TheirGender Male        Console WriteLine GetMyGender TheirGender Female        Console WriteLine GetMyGender TheirGender Unknown             static MyGender GetMyGender TheirGender theirGender            gt  theirGender switch                       TheirGender Male   gt  MyGender Male              TheirGender Female   gt  MyGender Female                  gt  throw new InvalidEnumArgumentException nameof theirGender    int theirGender  typeof TheirGender                 Here s a dotnet fiddle link with the above example  tl dr  Do not   Map enums by integer value Map enums by name  Do   Map enums explicitly using a switch statement Throw an exception when a value cannot be mapped rather than returning null Consider using extension methods

User · Answer

Based on Justin s answer above I came up with this            lt summary gt          Converts Enum Value to different Enum Value  by Value Name  See https   stackoverflow com a 31993512 6500501           lt  summary gt           lt typeparam name  TEnum  gt The type of the enum to convert to  lt  typeparam gt           lt param name  source  gt The source enum to convert from  lt  param gt           lt returns gt  lt  returns gt           lt exception cref  InvalidOperationException  gt  lt  exception gt      public static TEnum ConvertTo lt TEnum gt  this Enum source                try                       return  TEnum  Enum Parse typeof TEnum   source ToString    ignoreCase  true                     catch  ArgumentException aex                        throw new InvalidOperationException                                 Could not convert  source GetType   ToString      source ToString     to  typeof TEnum  ToString      aex

User · Answer

you could write a simple function like the following   public static MyGender ConvertTo TheirGender theirGender        switch theirGender                case TheirGender Male              break   return male         case TheirGender Female              break   return female         case TheirGender Unknown              break   return whatever

User · Answer

I wrote a set extension methods a while back that work for several different kinds of Enums  One in particular works for what you are trying to accomplish and handles Enums with the FlagsAttribute as well as Enums with different underlying types   public static tEnum SetFlags lt tEnum gt  this Enum e  tEnum flags  bool set  bool typeCheck   true  where tEnum   IComparable       if  typeCheck                if  e GetType      flags GetType                throw new ArgumentException  Argument is not the same type as this instance     flags               var flagsUnderlyingType   Enum GetUnderlyingType typeof tEnum         var firstNum   Convert ToUInt32 e       var secondNum   Convert ToUInt32 flags        if  set          firstNum    secondNum       else         firstNum  amp    secondNum       var newValue    tEnum Convert ChangeType firstNum  flagsUnderlyingType        if   typeCheck                var values   Enum GetValues typeof tEnum            var lastValue    tEnum values GetValue values Length - 1            if  newValue CompareTo lastValue   gt  0              return lastValue             return newValue      From there you can add other more specific extension methods   public static tEnum AddFlags lt tEnum gt  this Enum e  tEnum flags  where tEnum   IComparable       SetFlags e  flags  true      public static tEnum RemoveFlags lt tEnum gt  this Enum e  tEnum flags  where tEnum   IComparable       SetFlags e  flags  false       This one will change types of Enums like you are trying to do   public static tEnum ChangeType lt tEnum gt  this Enum e  where tEnum   IComparable       return SetFlags e  default tEnum   true  false       Be warned  though  that you CAN convert between any Enum and any other Enum using this method  even those that do not have flags  For example   public enum Turtle       None   0      Pink      Green      Blue      Black      Yellow     Flags  public enum WriteAccess   short      None   0     Read   1     Write   2     ReadWrite   3    static void Main string   args        WriteAccess access   WriteAccess ReadWrite      Turtle turtle   access ChangeType lt Turtle gt         The variable turtle will have a value of Turtle Blue   However  there is safety from undefined Enum values using this method  For instance   static void Main string   args        Turtle turtle   Turtle Yellow      WriteAccess access   turtle ChangeType lt WriteAccess gt         In this case  access will be set to WriteAccess ReadWrite  since the WriteAccess Enum has a maximum value of 3   Another side effect of mixing Enums with the FlagsAttribute and those without it is that the conversion process will not result in a 1 to 1 match between their values   public enum Letters       None   0      A      B      C      D      E      F      G      H     Flags  public enum Flavors       None   0      Cherry   1      Grape   2      Orange   4      Peach   8    static void Main string   args        Flavors flavors   Flavors Peach      Letters letters   flavors ChangeType lt Letters gt         In this case  letters will have a value of Letters H instead of Letters D  since the backing value of Flavors Peach is 8  Also  a conversion from Flavors Cherry   Flavors Grape to Letters would yield Letters C  which can seem unintuitive

User · Answer

Here s an extension method version if anyone is interested  public static TEnum ConvertEnum lt TEnum  gt  this Enum source                return  TEnum Enum Parse typeof TEnum   source ToString    true             Usage NewEnumType newEnum   oldEnumVar ConvertEnum lt NewEnumType gt

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public static TEnum ConvertByName lt TEnum gt  this Enum source  bool ignoreCase   false  where TEnum   struct          if limited by lack of generic enum constraint     if   typeof TEnum  IsEnum                throw new InvalidOperationException  enumeration type required                TEnum result      if   Enum TryParse source ToString    ignoreCase  out result                 throw new Exception  conversion failure                return result

User · Answer

You could write a simple generic extension method like this  public static T ConvertTo lt T gt  this object value                  where T   struct IConvertible       var sourceType   value GetType        if   sourceType IsEnum          throw new ArgumentException  Source type is not enum        if   typeof T  IsEnum          throw new ArgumentException  Destination type is not enum        return  T Enum Parse typeof T   value ToString

User · Answer

If we have   enum Gender       M   0      F   1      U   2     and  enum Gender2       Male   0      Female   1      Unknown   2     We can safely do  var gender   Gender M  var gender2      Gender2  int gender    Or even  var enumOfGender2Type    Gender2 0    If you want to cover the case where an enum on the right side of the     sign has more values than the enum on the left side - you will have to write your own method dictionary to cover that as others suggested

User · Answer

I know that s an old question and have a lot of answers  However I find that using a switch statement as in the accepted answer is somewhat cumbersome  so here are my 2 cents   My personal favorite method is to use a dictionary  where the key is the source enum and the value is the target enum - so in the case presented on the question my code would look like this   var genderTranslator   new Dictionary lt TheirGender  MyGender gt     genderTranslator Add TheirGender Male  MyGender Male   genderTranslator Add TheirGender Female  MyGender Female   genderTranslator Add TheirGender Unknown  MyGender Unknown       translate their to mine     var myValue   genderTranslator TheirValue       translate mine to their var TheirValue   genderTranslator  FirstOrDefault x   gt  x Value    myValue  Key     Of course  this can be wrapped in a static class and be used as an extension methods   public static class EnumTranslator        private static Dictionary lt TheirGender  MyGender gt  GenderTranslator   InitializeGenderTranslator         private static Dictionary lt TheirGender  MyGender gt  InitializeGenderTranslator                 var translator   new Dictionary lt TheirGender  MyGender gt             translator Add TheirGender Male  MyGender Male           translator Add TheirGender Female  MyGender Female           translator Add TheirGender Unknown  MyGender Unknown           return translator             public static MyGender Translate this TheirGender theirValue                return GenderTranslator theirValue              public static TheirGender Translate this MyGender myValue                return GenderTranslator FirstOrDefault x   gt  x Value    myValue  Key

User · Answer

To be thorough I normally create a pair of functions  one that takes Enum 1 and returns Enum 2 and another that takes Enum 2 and returns Enum 1  Each consists of a case statement mapping inputs to outputs and the default case throws an exception with a message complaining about an unexpected value   In this particular case you could take advantage of the fact that the integer values of Male and Female are the same  but I d avoid that as it s hackish and subject to breakage if either enum changes in the future

User · Answer

In case when the enum members have different values  you can apply something like this  public static MyGender  MapToMyGender this Gender gender        return gender switch               Gender Male   gt  MyGender Male          Gender Female   gt  MyGender Female          Gender Unknown   gt  null              gt  throw new InvalidEnumArgumentException   quot Invalid gender   gender  quot             Then you can call  var myGender   gender MapToMyGender    Update  This previous code works only with C  8  For older versions of C   you can use the switch statement instead of the switch expression  public static MyGender  MapToMyGender this Gender gender        switch  gender                case Gender Male               return MyGender Male          case Gender Female              return MyGender Female          case Gender Unknown              return null          default              throw new InvalidEnumArgumentException   quot Invalid gender   gender  quot

User · Answer

Using an extension method works quite neatly  when using the two conversion methods suggested by Nate   public static class TheirGenderExtensions       public static MyGender ToMyGender this TheirGender value                   insert switch statement here          public static class MyGenderExtensions       public static TheirGender ToTheirGender this MyGender value                   insert switch statement here           Obviously there s no need to use separate classes if you don t want to  My preference is to keep extension methods grouped by the classes structures enumerations they apply to

User · Answer

Given Enum1 value        then if you mean by name   Enum2 value2    Enum2  Enum Parse typeof Enum2   value ToString       If you mean by numeric value  you can usually just cast   Enum2 value2    Enum2 value     with the cast  you might want to use Enum IsDefined to check for valid values  though

[c#] convert an enum to another type of enum

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