Handle unary operator on enums (#265)

* Handle unary operator on enums
Fixes #261

src/DynamicExpresso.Core/Parsing/Parser.cs

@@ -641,6 +641,11 @@ private Expression GenerateUnary(ExpressionType unaryType, Expression expr)
 			if (IsDynamicExpression(expr))
 				return GenerateUnaryDynamic(unaryType, expr);
 
+			// enum unary operations are not resolved properly by Linq
+			var unaryOps = new[] { ExpressionType.OnesComplement };
+			if (expr.Type.IsEnum && unaryOps.Contains(unaryType))
+				return GenerateUnaryEnums(unaryType, expr);
+
 			// find the overloaded unary operator
 			string opName;
 			switch (unaryType)
@@ -664,6 +669,14 @@ private Expression GenerateUnary(ExpressionType unaryType, Expression expr)
 			return Expression.MakeUnary(unaryType, expr, null, operatorMethod);
 		}
 
+		private Expression GenerateUnaryEnums(ExpressionType unaryType, Expression expr)
+		{
+			var enumType = expr.Type;
+			var underlyingType = enumType.GetEnumUnderlyingType();
+			expr = Expression.Convert(expr, underlyingType);
+			return Expression.MakeUnary(unaryType, expr, enumType);
+		}
+
 		private Expression GenerateUnaryDynamic(ExpressionType unaryType, Expression expr)
 		{
 			var binder = Microsoft.CSharp.RuntimeBinder.Binder.UnaryOperation(

test/DynamicExpresso.UnitTest/GithubIssues.cs

@@ -662,6 +662,21 @@ public class PageType
 			public string PageName { get; set; }
 			public int VisualCount { get; set; }
 		}
+
+		[Test]
+		public void GitHub_Issue_261()
+		{
+			var target = new Interpreter();
+			target.Reference(typeof(RegexOptions));
+			target.Reference(typeof(DateTimeKind));
+
+			var result = target.Eval<RegexOptions>("~RegexOptions.None");
+			Assert.AreEqual(~RegexOptions.None, result);
+
+			// DateTimeKind doesn't have the Flags attribute: the bitwise operation returns an integer
+			var result2 = target.Eval<DateTimeKind>("~DateTimeKind.Local");
+			Assert.AreEqual((DateTimeKind)(-3), result2);
+		}
 	}
 
 	internal static class GithubIssuesTestExtensionsMethods