gistfile1.cs

// Languages\Ruby\Ruby\Builtins\RubyEncoding.cs
        public static RubyEncoding/*!*/ GetRubyEncoding(Encoding/*!*/ encoding) {
            ContractUtils.RequiresNotNull(encoding, "encoding");
            if (encoding == BinaryEncoding.Instance) {
                return Binary;
            } else if (encoding.ToString() == Encoding.UTF8.ToString()) {
                return UTF8;
            } else {
                throw new ArgumentException(String.Format("Unknown encoding: '{0}'", encoding));
            }
        }

/*
There's a tiny problem there when running IronRuby in Silverlight; it fails when the encoding is an instance of KCoding:

ArgumentException: Unknown encoding: 'KCODE (UTF8)'
*/

//This...
            } else if (encoding.ToString() == Encoding.UTF8.ToString()) {

// ... should be replaced with this:
            } else if (encoding is KCoding || encoding == Encoding.UTF8) {

/*
The expression "Encoding.UTF8.ToString()" will always return "System.Encoding.UTF8",
so it doesn't make sense to test against that.
*/