C# Blooper №11: Zero to Enum conversion weirdness

Before reading any further, please read the disclaimer in the C# Bloopers post.

When you assign an enum to int, you have to cast it. That's good. When you assign an int to enum, you also have to cast it. That's also good. But if you assign zero to an enum, you don't have to cast it! Go figure.

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namespace Test11
{
    class Test
    {
        public enum myenum
        {
            a, b, c
        }

        void test_myenum( myenum f, int i )
        {
            i = (int)myenum.a; //need to cast; that's good.
            f = (myenum)5; //need to cast; that's still good.
            f = 0; //wtf? no need to cast?
        }
    }
}