convert an array of enums into a generic array of enums

Question

How can I convert an array of enums into a generic array of enums in c#.

To be clear:

Given:

public enum PrimaryColor
{
    red = 0,
    blue = 1,
    yellow = 3
}

public enum SecondaryColor
{
    green = 0,
    purple = 1,
    orange = 2
}

I want to do something like this:

public class MyClass
{
    public static void Main()
    {
        PrimaryColor[] pca = {PrimaryColor.blue, PrimaryColor.yellow};
        SecondaryColor[] sca = {SecondaryColor.purple, SecondaryColor.orange};

        Enum[] enumArray = pca;
    }

}

which leads to a compiler error of:

Cannot implicitly convert type 'PrimaryColor[]' to 'System.Enum[]'

I could use linq or some more iterative process, but I wonder if there is a better cast I could use instead.

I have edited your title. Please see, "Should questions include “tags” in their titles?", where the consensus is "no, they should not". — John Saunders
– John Saunders, Commented Feb 1, 2013 at 16:19

Sergey Berezovskiy · Accepted Answer · 2013-02-01 16:34:25Z

3

You can do it iteratively only

Enum[] enumArray = Array.ConvertAll(pca, item => (Enum)item);

Or (less efficient but Linq!)

Enum[] enumArray = pca.Cast<Enum>().ToArray();

Why you can't simply cast arrays? Because in C# covariance enabled only for arrays of reference types (enums are value types). So, with class Foo you can do:

Foo[] foos = new Foo[10];
object[] array = (object[])foos;

edited Feb 1, 2013 at 16:34

answered Feb 1, 2013 at 16:15

Sergey Berezovskiy

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4 Comments

Eric Lippert Over a year ago

An interesting oddity in the type system is that the CLR type system allows array covariance on compatible value types. For example, uint[] is convertible to int[]. C# as you correctly note only allows array covariance if both types are reference types. Which means that it is possible that in C#, the cast (int[])(object)x will succeed at runtime, but the same cast without object would fail at compile time.

Sergey Berezovskiy Over a year ago

@EricLippert thanks, great comment! Didn't know that array covariance on compatible value types is allowed. Btw why Enum does not considered compatible for example above? I.e. I can do (int[])(object)pca, but I can't do (Enum[])(object)pca. Also looks like there is a bug in VS2012 s4.postimage.org/c17b94me5/array_covariance.png :)

Eric Lippert Over a year ago

Enum is a reference type; it's a boxed enum. The array therefore has to be full of references, not full of values.

Eric Lippert Over a year ago

See blogs.msdn.com/b/ericlippert/archive/2009/09/24/… and stackoverflow.com/questions/1178973/… for more details on how CLR variance differs from C# variance.

daryal · Accepted Answer · 2013-02-01 16:18:54Z

0

PrimaryColor[] pca = { PrimaryColor.blue, PrimaryColor.yellow };
SecondaryColor[] sca = { SecondaryColor.purple, SecondaryColor.orange };

Enum[] enumArray = pca.Select(q => q as Enum).ToArray();

Or;

for (int i=0; i<pca.Count();i++)
{
    enumArray[i] = pca[i];                
}

answered Feb 1, 2013 at 16:18

daryal

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