Converting an integer to a boxed enum type only known at runtime

Posted by Marc Gravell on Stack Overflow See other posts from Stack Overflow or by Marc Gravell
Published on 2010-04-17T21:47:35Z Indexed on 2010/04/17 21:53 UTC
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Imagine we have an enum:

enum Foo { A=1,B=2,C=3 }

If the type is known at compile-time, a direct cast can be used to change between the enum-type and the underlying type (usually int):

static int GetValue() { return 2; }
...
Foo foo = (Foo)GetValue(); // becomes Foo.B

And boxing this gives a box of type Foo:

object o1 = foo;
Console.WriteLine(o1.GetType().Name); // writes Foo

(and indeed, you can box as Foo and unbox as int, or box as int and unbox as Foo quite happily)

However (the problem); if the enum type is only known at runtime things are... trickier. It is obviously trivial to box it as an int - but can I box it as Foo? (Ideally without using generics and MakeGenericMethod, which would be ugly). Convert.ChangeType throws an exception. ToString and Enum.Parse works, but is horribly inefficient.

I could look at the defined values (Enum.GetValues or Type.GetFields), but that is very hard for [Flags], and even without would require getting back to the underlying-type first (which isn't as hard, thankfully).

But; is there a more direct to get from a value of the correct underlying-type to a box of the enum-type, where the type is only known at runtime?

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