Reduce value type boxing in interop calls (#787)

* Reduce value type boxing in interop calls

* special case common bool and int property access
* use abstract class instead of interface do reduce virtual dispatch cost

* code tweaks

Author: lahma

Fluid/Accessors/PropertyInfoAccessor.cs

@@ -1,17 +1,18 @@
 using System.Reflection;
 using System.Reflection.Emit;
+using Fluid.Values;
 
 namespace Fluid.Accessors
 {
     public sealed class PropertyInfoAccessor : IMemberAccessor
     {
-        private readonly IInvoker _invoker;
+        private readonly Invoker _invoker;
 
         public PropertyInfoAccessor(PropertyInfo propertyInfo)
         {
             Delegate d;
 
-            if (!propertyInfo.DeclaringType.IsValueType)
+            if (!propertyInfo.DeclaringType?.IsValueType == true)
             {
                 var delegateType = typeof(Func<,>).MakeGenericType(propertyInfo.DeclaringType, propertyInfo.PropertyType);
                 d = propertyInfo.GetGetMethod().CreateDelegate(delegateType);
@@ -21,7 +22,7 @@ public PropertyInfoAccessor(PropertyInfo propertyInfo)
                 // We can't create an open delegate on a struct (dotnet limitation?), so instead create custom delegates
                 // https://sharplab.io/#v2:EYLgtghglgdgNAFxAJwK7wCYgNQB8ACATAAwCwAUEQIwX7EAE+VAdACLIQDusA5gNwUKANwjJ6ABwCSMAGYB7egF56CAJ7iApnJkAKAApzYCAJTMA4hoR7kczcjU6ARAA1HxgeRFiMhJROny5pYWCACylgAWchg6pgDCyBoQCBqsGgA2GjzJGjpqmto6+ACsADwGRnD0RgB8xu4UQA==
                 // Instead we generate IL to access the backing field directly
-                
+
                 d = GetGetter(propertyInfo.DeclaringType, propertyInfo.Name);
             }
 
@@ -30,58 +31,76 @@ public PropertyInfoAccessor(PropertyInfo propertyInfo)
                 _invoker = null;
             }
 
-            var invokerType = typeof(Invoker<,>).MakeGenericType(propertyInfo.DeclaringType, propertyInfo.PropertyType);
-            _invoker = Activator.CreateInstance(invokerType, [d]) as IInvoker;
-        }
+            Type invokerType;
+            if (propertyInfo.PropertyType == typeof(bool))
+            {
+                invokerType = typeof(BooleanInvoker<>).MakeGenericType(propertyInfo.DeclaringType);
+            }
+            else if (propertyInfo.PropertyType == typeof(int))
+            {
+                invokerType = typeof(Int32Invoker<>).MakeGenericType(propertyInfo.DeclaringType);
+            }
+            else
+            {
+                invokerType = typeof(Invoker<,>).MakeGenericType(propertyInfo.DeclaringType, propertyInfo.PropertyType);
+            }
 
-        public object Get(object obj, string name, TemplateContext ctx)
-        {
-            return _invoker?.Invoke(obj);
+            _invoker = (Invoker) Activator.CreateInstance(invokerType, [d]);
         }
 
+        public object Get(object obj, string name, TemplateContext ctx) => _invoker.Invoke(obj);
+
         private static Delegate GetGetter(Type declaringType, string fieldName)
         {
-            string[] names = [fieldName.ToLowerInvariant(), $"<{fieldName}>k__BackingField", "_" + fieldName.ToLowerInvariant()];
-
-            var field = names
-                .Select(n => declaringType.GetField(n, BindingFlags.Instance | BindingFlags.NonPublic))
-                .FirstOrDefault(x => x != null);
+            string[] names = [fieldName.ToLowerInvariant(), $"<{fieldName}>k__BackingField", $"_{fieldName.ToLowerInvariant()}"];
 
-            if (field == null)
+            foreach (var n in names)
             {
-                return null;
-            }
+                var field = declaringType.GetField(n, BindingFlags.Instance | BindingFlags.NonPublic);
+                if (field == null)
+                {
+                    continue;
+                }
 
-            var parameterTypes = new[] { typeof(object), declaringType };
+                var parameterTypes = new[] { typeof(object), declaringType };
 
-            var method = new DynamicMethod(fieldName + "Get", field.FieldType, parameterTypes, typeof(PropertyInfoAccessor).Module, true);
+                var method = new DynamicMethod(fieldName + "Get", field.FieldType, parameterTypes, typeof(PropertyInfoAccessor).Module, true);
 
-            var emitter = method.GetILGenerator();
-            emitter.Emit(OpCodes.Ldarg_1);
-            emitter.Emit(OpCodes.Ldfld, field);
-            emitter.Emit(OpCodes.Ret);
+                var emitter = method.GetILGenerator();
+                emitter.Emit(OpCodes.Ldarg_1);
+                emitter.Emit(OpCodes.Ldfld, field);
+                emitter.Emit(OpCodes.Ret);
 
-            return method.CreateDelegate(typeof(Func<,>).MakeGenericType(declaringType, field.FieldType));
+                return method.CreateDelegate(typeof(Func<,>).MakeGenericType(declaringType, field.FieldType));
+            }
+
+            return null;
         }
 
-        private interface IInvoker
+        private abstract class Invoker
         {
-            object Invoke(object target);
+            public abstract object Invoke(object target);
         }
 
-        private sealed class Invoker<T, TResult> : IInvoker
+        private sealed class Invoker<T, TResult>(Delegate d) : Invoker
         {
-            private readonly Func<T, TResult> _d;
+            private readonly Func<T, TResult> _d = (Func<T, TResult>) d;
 
-            public Invoker(Delegate d)
-            {
-                _d = (Func<T, TResult>)d;
-            }
+            public override object Invoke(object target) => _d((T) target);
+        }
 
-            public object Invoke(object target)
-            {
-                return _d((T)target);
-            }
+        private sealed class BooleanInvoker<T>(Delegate d) : Invoker
+        {
+            private readonly Func<T, bool> _d = (Func<T, bool>) d;
+
+            public override object Invoke(object target) => _d((T) target) ? BooleanValue.True : BooleanValue.False;
+        }
+
+        private sealed class Int32Invoker<T>(Delegate d) : Invoker
+        {
+            private readonly Func<T, int> _d = (Func<T, int>) d;
+
+            public override object Invoke(object target) => NumberValue.Create(_d((T) target));
         }
     }
 }