gistfile1.cs

[RubyClass]
public class Foo {
  private MutableString _bar =  MutableString.Create("");

  [RubyMethod("bar")]
  public static MutableString GetBar(RubyContext context, Foo self) {
    return self._bar;
  }

  [RubyMethod("bar=")]
  public static MutableString GetBar(RubyContext context, Foo self, MutableString value) {
    self._bar = value;
  }
}