Optimize memory allocations when attaching styles.

src/Avalonia.Styling/Styling/Setter.cs

@@ -78,8 +78,6 @@ namespace Avalonia.Styling
         {
             Contract.Requires<ArgumentNullException>(control != null);
 
-            var description = style?.ToString();
-
             if (Property == null)
             {
                 throw new InvalidOperationException("Setter.Property must be set.");
@@ -107,6 +105,8 @@ namespace Avalonia.Styling
                 }
                 else
                 {
+                    var description = style?.ToString();
+
                     var activated = new ActivatedValue(activator, value, description);
                     return control.Bind(Property, activated, BindingPriority.StyleTrigger);
                 }

src/Avalonia.Styling/Styling/Style.cs

@@ -116,13 +116,21 @@ namespace Avalonia.Styling
                 if (match.IsMatch)
                 {
                     var controlSubscriptions = GetSubscriptions(control);
-                    
-                    var subs = new CompositeDisposable(Setters.Count + Animations.Count);
 
-                    if (control is Animatable animatable)
+                    var animatable = control as Animatable;
+
+                    var setters = Setters;
+                    var settersCount = setters.Count;
+                    var animations = Animations;
+                    var animationsCount = animations.Count;
+
+                    var subs = new CompositeDisposable(settersCount + (animatable != null ? animationsCount : 0) + 1);
+
+                    if (animatable != null)
                     {
-                        foreach (var animation in Animations)
+                        for (var i = 0; i < animationsCount; i++)
                         {
+                            var animation = animations[i];
                             var obsMatch = match.Activator;
 
                             if (match.Result == SelectorMatchResult.AlwaysThisType ||
@@ -133,17 +141,19 @@ namespace Avalonia.Styling
 
                             var sub = animation.Apply(animatable, null, obsMatch);
                             subs.Add(sub);
-                        } 
+                        }
                     }
 
-                    foreach (var setter in Setters)
+                    for (var i = 0; i < settersCount; i++)
                     {
+                        var setter = setters[i];
                         var sub = setter.Apply(this, control, match.Activator);
                         subs.Add(sub);
                     }
 
+                    subs.Add(Disposable.Create((subs, Subscriptions) , state =>  state.Subscriptions.Remove(state.subs)));
+
                     controlSubscriptions.Add(subs);
-                    controlSubscriptions.Add(Disposable.Create(() => Subscriptions.Remove(subs)));
                     Subscriptions.Add(subs);
                 }
 
@@ -151,18 +161,23 @@ namespace Avalonia.Styling
             }
             else if (control == container)
             {
+                var setters = Setters;
+                var settersCount = setters.Count;
+
                 var controlSubscriptions = GetSubscriptions(control);
 
-                var subs = new CompositeDisposable(Setters.Count);
+                var subs = new CompositeDisposable(settersCount + 1);
 
-                foreach (var setter in Setters)
+                for (var i = 0; i < settersCount; i++)
                 {
+                    var setter = setters[i];
                     var sub = setter.Apply(this, control, null);
                     subs.Add(sub);
                 }
 
+                subs.Add(Disposable.Create((subs, Subscriptions), state => state.Subscriptions.Remove(state.subs)));
+
                 controlSubscriptions.Add(subs);
-                controlSubscriptions.Add(Disposable.Create(() => Subscriptions.Remove(subs)));
                 Subscriptions.Add(subs);
                 return true;
             }

src/Avalonia.Styling/Styling/Styles.cs

@@ -239,8 +239,10 @@ namespace Avalonia.Styling
         /// <inheritdoc/>
         public bool Remove(IStyle item) => _styles.Remove(item);
 
+        public AvaloniaList<IStyle>.Enumerator GetEnumerator() => _styles.GetEnumerator();
+
         /// <inheritdoc/>
-        public IEnumerator<IStyle> GetEnumerator() => _styles.GetEnumerator();
+        IEnumerator<IStyle> IEnumerable<IStyle>.GetEnumerator() => _styles.GetEnumerator();
 
         /// <inheritdoc/>
         IEnumerator IEnumerable.GetEnumerator() => _styles.GetEnumerator();