c# - Generics, enums and custom attributes - is it possible? -

apologies amount of code, easier explain way.

i have custom attribute customuserdata implemented follows:

public class customuserdata : attribute {    public customuserdata(object auserdata)    {       userdata = auserdata;    }    public object userdata { get; set; } } 

and extension method enums as:

public static class enumextensions {     public static tattribute getattribute<tattribute>(this enum avalue) tattribute : attribute     {         type type = avalue.gettype();         string name = enum.getname(type, avalue);         return type.getfield(name)                    .getcustomattributes(false)                    .oftype<tattribute>()                    .singleordefault();     }      public static object getcustomuserdata(this enum avalue)     {         customuserdata uservalue = getattribute<customuserdata>(avalue);         return uservalue != null ? uservalue.userdata : null;     } } 

i have helper class serializes/deserializes enum has custom data associated follows:

public static class parameterdisplaymodeenumlisthelper {     public static list<parameterdisplaymodeenum> fromdatabase(string adisplaymodestring)     {         //default behaviour         list<parameterdisplaymodeenum> result = new list<parameterdisplaymodeenum>();          //split string list list of strings         list<string> listofdisplaymodes = new list<string>(adisplaymodestring.split(','));          //iterate enum looking matches in list         foreach (parameterdisplaymodeenum displaymodeenum in enum.getvalues(typeof (parameterdisplaymodeenum)))         {             if (listofdisplaymodes.findindex(item => item == (string)displaymodeenum.getcustomuserdata()) >= 0)             {                 result.add(displaymodeenum);             }         }          return result;     }      public static string todatabase(list<parameterdisplaymodeenum> adisplaymodelist)     {         string result = string.empty;          foreach (parameterdisplaymodeenum listitem in adisplaymodelist)         {             if (result != string.empty)                 result += ",";             result += listitem.getcustomuserdata();         }          return result;     } } 

however specific parameterdisplaymodeenum , have bunch of enums need treat way serialization/deserialization prefer have generic such as:

public static class enumlisthelper<tenum> {     public static list<tenum> fromdatabase(string adisplaymodestring)     {         //default behaviour         list<tenum> result = new list<tenum>();          //split string list list of strings         list<string> listofdisplaymodes = new list<string>(adisplaymodestring.split(','));          //iterate enum looking matches in list         foreach (tenum displaymodeenum in enum.getvalues(typeof (tenum)))         {             if (listofdisplaymodes.findindex(item => item == (string)displaymodeenum.getcustomuserdata()) >= 0)             {                 result.add(displaymodeenum);             }         }          return result;     }      public static string todatabase(list<tenum> adisplaymodelist)     {         string result = string.empty;          foreach (tenum listitem in adisplaymodelist)         {             if (result != string.empty)                 result += ",";             result += listitem.getcustomuserdata();         }          return result;     } } 

however not work getcustomuserdata() cannot invoked. suggestions? cannot change use of custom attribute or use of enums. looking generic way serialization/deserialization without having write concrete list helper class each time.

all suggestions appreciated.

try code:

public static class enumlisthelper {     private static void ensureisenum<tenum>()     {         if (!typeof(tenum).isenum)             throw new invalidoperationexception(string.format("the {0} type not enum.", typeof(tenum)));     }      public static list<tenum> fromdatabase<tenum>(string adisplaymodestring)         tenum : struct     {         ensureisenum<tenum>();         //default behaviour         list<tenum> result = new list<tenum>();          //split string list list of strings         list<string> listofdisplaymodes = new list<string>(adisplaymodestring.split(','));          //iterate enum looking matches in list         foreach (enum displaymodeenum in enum.getvalues(typeof(tenum)))         {             if (listofdisplaymodes.findindex(item => item == (string)displaymodeenum.getcustomuserdata()) >= 0)             {                 result.add((tenum)(object)displaymodeenum);             }         }          return result;     }      public static string todatabase<tenum>(list<tenum> adisplaymodelist)         tenum : struct     {         ensureisenum<tenum>();         string result = string.empty;          foreach (var listitem in adisplaymodelist.oftype<enum>())         {             if (result != string.empty)                 result += ",";             result += listitem.getcustomuserdata();         }          return result;     } }  var fromdatabase = enumlisthelper.fromdatabase<testenum>("test"); enumlisthelper.todatabase(fromdatabase); 

update 0

to clear, because cannot restrict generics enum should check type tenum enum , throw exception if not. when use fromdatabase method know tenum enum, , can write code cast enum specified tenum:

result.add((tenum)(object)displaymodeenum) 

in todatabase method know tenum enum , can write code convert tenum enum type:

adisplaymodelist.oftype<enum>()