perf: get rid of a couple closures (#103)

* perf: get rid of a couple closures

* replace variable abbreviation with proper name

Co-authored-by: Glenn <[email protected]>

Author: cabauman

src/ReactiveMarbles.PropertyChanged/GetMemberFuncCache.cs

@@ -12,25 +12,23 @@ namespace ReactiveMarbles.PropertyChanged
     internal static class GetMemberFuncCache<TFrom, TReturn>
     {
 #if !UIKIT
-        private static readonly
-            ConcurrentDictionary<(Type FromType, string MemberName), Func<TFrom, TReturn>> Cache
-                = new ConcurrentDictionary<(Type, string), Func<TFrom, TReturn>>();
+        private static readonly ConcurrentDictionary<MemberInfo, Func<TFrom, TReturn>> Cache = new(new MemberFuncCacheKeyComparer());
 #endif
 
         public static Func<TFrom, TReturn> GetCache(MemberInfo memberInfo)
         {
 #if UIKIT
-                switch (memberInfo)
-                {
-                    case PropertyInfo propertyInfo:
-                        return input => (TReturn)propertyInfo.GetValue(input);
-                    case FieldInfo fieldInfo:
-                        return input => (TReturn)fieldInfo.GetValue(input);
-                    default:
-                        throw new ArgumentException($"Cannot handle member {memberInfo.Name}", nameof(memberInfo));
-                }
+            switch (memberInfo)
+            {
+                case PropertyInfo propertyInfo:
+                    return input => (TReturn)propertyInfo.GetValue(input);
+                case FieldInfo fieldInfo:
+                    return input => (TReturn)fieldInfo.GetValue(input);
+                default:
+                    throw new ArgumentException($"Cannot handle member {memberInfo.Name}", nameof(memberInfo));
+            }
 #else
-            return Cache.GetOrAdd((memberInfo.DeclaringType, memberInfo.Name), _ =>
+            return Cache.GetOrAdd(memberInfo, static memberInfo =>
             {
                 var instance = Expression.Parameter(typeof(TFrom), "instance");
 

src/ReactiveMarbles.PropertyChanged/MemberFuncCacheKeyComparer.cs

@@ -0,0 +1,22 @@
+// Copyright (c) 2019-2020 ReactiveUI Association Incorporated. All rights reserved.
+// ReactiveUI Association Incorporated licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for full license information.
+
+using System.Collections.Generic;
+using System.Reflection;
+
+namespace ReactiveMarbles.PropertyChanged
+{
+    internal sealed class MemberFuncCacheKeyComparer : IEqualityComparer<MemberInfo>
+    {
+        public bool Equals(MemberInfo x, MemberInfo y)
+        {
+            return (x.DeclaringType, x.Name) == (y.DeclaringType, y.Name);
+        }
+
+        public int GetHashCode(MemberInfo obj)
+        {
+            return (obj.DeclaringType, obj.Name).GetHashCode();
+        }
+    }
+}

src/ReactiveMarbles.PropertyChanged/NotifyPropertyChangedExtensions.cs

@@ -74,17 +74,17 @@ public static IObservable<TReturn> WhenPropertyValueChanges<TObj, TReturn>(
 
                 if (i == expressionChain.Count - 1)
                 {
-                    var function = GetMemberFuncCache<INotifyPropertyChanged, TReturn>.GetCache(memberInfo);
-                    return currentObservable
-                        .Where(parent => parent.Value != null)
-                        .Select(parent => GenerateObservable(parent.Value, memberInfo, function))
+                    return Observable.Return(memberInfo)
+                        .CombineLatest(currentObservable, (memberInfo, parent) => (memberInfo, sender: parent.Sender, value: parent.Value))
+                        .Where(x => x.value != null)
+                        .Select(x => GenerateObservable(x.value, x.memberInfo, GetMemberFuncCache<INotifyPropertyChanged, TReturn>.GetCache(x.memberInfo)))
                         .Switch();
                 }
 
-                var iFunction = GetMemberFuncCache<INotifyPropertyChanged, INotifyPropertyChanged>.GetCache(memberInfo);
-                currentObservable = currentObservable
-                    .Where(parent => parent.Value != null)
-                    .Select(parent => GenerateObservable(parent.Value, memberInfo, iFunction))
+                currentObservable = Observable.Return(memberInfo)
+                    .CombineLatest(currentObservable, (memberInfo, parent) => (memberInfo, sender: parent.Sender, value: parent.Value))
+                    .Where(x => x.value != null)
+                    .Select(x => GenerateObservable(x.value, x.memberInfo, GetMemberFuncCache<INotifyPropertyChanged, INotifyPropertyChanged>.GetCache(x.memberInfo)))
                     .Switch();
 
                 i++;