gistfile1.cs

// Instead of writing:
//   if( a == "abc" || a == "xyz" || a == "123" ) { ... }
//   if( opt != Options.Opt1 && opt != Options.Opt2 && opt != Options.Opt3 ) { ... }
// We can write:
//   if( a.OneOf("abc", "xyz", 123") ) { ... }
//   if( opt.NoneOf(Options.Opt1, Options.Opt2, Options.Opt3) ) { ... }

    public static class ObjectExtensions
    {
        public static bool OneOf<T>(this T self, params T[] values)
        {
            return !IsNull(self) && values.Any(value => self.Equals(value));
        }

        public static bool NoneOf<T>(this T self, params T[] values)
        {
            return !IsNull(self) && !self.OneOf(values);
        }

        private static bool IsNull<T>(T self)
        {
            object def = default(T);
            return def == null && object.Equals(self, def); 
        }
    }