From 92035ffdba2aebef5c6da7b81cff79e54117f48a Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Wed, 9 Mar 2016 19:52:08 +0100
Subject: [PATCH] Don't CombineLatest if no need.

---
 src/Perspex.Styling/Styling/StyleActivator.cs | 34 +++++++++++++++----
 1 file changed, 28 insertions(+), 6 deletions(-)

diff --git a/src/Perspex.Styling/Styling/StyleActivator.cs b/src/Perspex.Styling/Styling/StyleActivator.cs
index dd2601e0bb..05b97a11ec 100644
--- a/src/Perspex.Styling/Styling/StyleActivator.cs
+++ b/src/Perspex.Styling/Styling/StyleActivator.cs
@@ -17,18 +17,40 @@ namespace Perspex.Styling
 
     public static class StyleActivator
     {
-        public static IObservable<bool> And(IEnumerable<IObservable<bool>> inputs)
+        public static IObservable<bool> And(IList<IObservable<bool>> inputs)
         {
-            return inputs.CombineLatest()
-                .Select(values => values.All(x => x))
-                .DistinctUntilChanged();
+            if (inputs.Count == 0)
+            {
+                throw new ArgumentException("StyleActivator.And inputs may not be empty.");
+            }
+            else if (inputs.Count == 1)
+            {
+                return inputs[0];
+            }
+            else
+            {
+                return inputs.CombineLatest()
+                    .Select(values => values.All(x => x))
+                    .DistinctUntilChanged();
+            }
         }
 
-        public static IObservable<bool> Or(IEnumerable<IObservable<bool>> inputs)
+        public static IObservable<bool> Or(IList<IObservable<bool>> inputs)
         {
-            return inputs.CombineLatest()
+            if (inputs.Count == 0)
+            {
+                throw new ArgumentException("StyleActivator.Or inputs may not be empty.");
+            }
+            else if (inputs.Count == 1)
+            {
+                return inputs[0];
+            }
+            else
+            {
+                return inputs.CombineLatest()
                 .Select(values => values.Any(x => x))
                 .DistinctUntilChanged();
+            }
         }
     }
 }