#93 shift selection

OpenRa.Game/Exts.cs

@@ -1,4 +1,8 @@
 
+using System.Windows.Forms;
+using System.Collections.Generic;
+using System.Linq;
+
 namespace OpenRa.Game
 {
 	static class Exts
@@ -7,5 +11,16 @@ namespace OpenRa.Game
 		{
 			return string.Format(fmt, args);
 		}
+
+		public static bool HasModifier(this Keys k, Keys mod)
+		{
+			return (k & mod) == mod;
+		}
+
+		public static IEnumerable<T> SymmetricDifference<T>(this IEnumerable<T> xs, IEnumerable<T> ys)
+		{
+			// this is probably a shockingly-slow way to do this, but it's concise.
+			return xs.Except(ys).Concat(ys.Except(xs));
+		}
 	}
 }