c# - Avoid having to cast with generics and a list of custom data -


i have following code supporting list of different types :

public enum etype {     tint,     tstring,     tdatetime }  public interface icustomtype<out t> {     t value { get; } }  public abstract class differenttype {     protected differenttype(etype type, string mnemonic)     {         type = type;         mnemonic = mnemonic;     }      public string mnemonic { get; private set; }      public etype type { get; private set; } }  public class datetimetype : differenttype, icustomtype<datetime> {     public datetimetype(datetime value, string mnemonic)         : base(etype.tdatetime, mnemonic)     {         value = value;     }      public datetime value { get; private set; } }  public class inttype : differenttype, icustomtype<int> {     public inttype(int value, string mnemonic)         : base(etype.tint, mnemonic)     {         value = value;     }      public int value { get; private set; } }  public class stringtype : differenttype, icustomtype<string> {     public stringtype(string value, string mnemonic)         : base(etype.tstring, mnemonic)     {         value = value;     }      public string value { get; private set; } }  public static class utilvalue {     public static t getvalue<t>(differenttype customtype)     {         return ((icustomtype<t>)customtype).value;     } }  public class testtypes2 {     public testtypes2()     {         var values = new list<differenttype> { getint(), getstring(), getdate() };          foreach (var in values)         {             switch (i.type)             {                 case etype.tint:                     int resint = utilvalue.getvalue<int>(i);                     break;                  case etype.tstring:                     string resstring = utilvalue.getvalue<string>(i);                     break;                  case etype.tdatetime:                     datetime resdatetime = utilvalue.getvalue<datetime>(i);                     break;             }         }     }      private datetimetype getdate()     {         return new datetimetype(new datetime(2000, 1, 1), "mnemonicdate");     }      private inttype getint()     {         return new inttype(5, "mnemonicint");     }      private stringtype getstring()     {         return new stringtype("ok", "mnemonicstring");     } }

and avoid cast @ line return ((icustomtype<t>)customtype).value; in utilvalue class, idea how can rid of while still keeping design?

i not sure if cast expensive do? guess most certainly.

visitor-pattern example:

interface idifferenttypevisitor {     void visit(datetimetype dt);     void visit(stringtype st); }  class differenttype {     public abstract void accept(idifferenttypevisitor visitor); }  class datetimetype : differenttype {     public void accept(idifferenttypevisitor visitor)     {         visitor.visit(this);     } }  class stringtype : differenttype {     public void accept(idifferenttypevisitor visitor)     {         visitor.visit(this);     } }  class somevisitor : idifferenttypevisitor {     public void visit(datetimetype dt)     {         //datetime resdatetime = dt.value; or similar     }      public void visit(stringtype st)     {         //string resstring = st.value; or similar     } }  public class testtypes2 {     public testtypes2()     {         var values = new list<differenttype> { /* content */ };         var visitor = new somevisitor();          foreach (var in values)         {             i.accept(visitor);         }     } }

in c# 4 dynamic it's possible save code adding differenttype:

public void accept(idifferenttypevisitor visitor) {     visitor.visit((dynamic)this); }

and delete other accept methods. hurts performance looks better ;-)


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