有没有一种方法可以在一个自定义枚举集合与另一个自定义枚举集合之间进行转换？

Question

We already know we can convert an enum to another type of enum , so the following compiles:

public class EnumTest
{
   enum Enum1 { Foo };
   enum Enum2 { Foo };
   void Test () 
   {
       System.Enum e = new Enum2();   // compiles
       Enum1 e1 = (Enum1)new Enum2(); // compiles with an explicit cast
   }
}

But this doesn't compile:

public class EnumTest
{
   enum Enum1 { Foo };
   enum Enum2 { Foo };
   void Test () 
   {
       List<System.Enum> eList = new List<Enum2>();         // doesn't compile
       List<Enum1> e1List = (List<Enum1>)new List<Enum2>(); // doesn't compile
   }
}

Is that a covariance issue? If not, is there a way to make it work?

Answer 1

It's not a co -variance issue, it's a variance issue. Enums are value types and co-variance is not supported for value types. And List<T> is a class , not an interface or delegate . Co-variance is only supported for interfaces and delegates.

You have to cast/convert the elements in the lists:

List<Enum2> list2 = ...
List<System.Enum> eList = list2.Cast<System.Enum>().ToList();

But this of course results in a new list. eList is a different instance than list2 .

Answer 2

You can't cast like that, Enum1 and Enum2 are completely different things. You can do it with some simple Linq though. For example:

List<Enum2> eList = new List<Enum2>
{ 
    Enum2.Foo 
};

List<Enum1> e1List = eList
    .Select(x => (Enum1)x)
    .ToList();

Note this is using a straight case, but you might want to use the conversion function from the question you linked.