1 files changed, 118 insertions, 0 deletions
diff --git a/csharp/ProtocolBuffers/FieldAccess/ReflectionUtil.cs b/csharp/ProtocolBuffers/FieldAccess/ReflectionUtil.cs
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+++ b/csharp/ProtocolBuffers/FieldAccess/ReflectionUtil.cs
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+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.
+// http://code.google.com/p/protobuf/
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+using System;
+using System.Reflection;
+
+namespace Google.ProtocolBuffers.FieldAccess {
+
+  /// <summary>
+  /// The methods in this class are somewhat evil, and should not be tampered with lightly.
+  /// Basically they allow the creation of relatively weakly typed delegates from MethodInfos
+  /// which are more strongly typed. They do this by creating an appropriate strongly typed
+  /// delegate from the MethodInfo, and then calling that within an anonymous method.
+  /// Mind-bending stuff (at least to your humble narrator) but the resulting delegates are
+  /// very fast compared with calling Invoke later on.
+  /// </summary>
+  internal static class ReflectionUtil {
+
+    /// <summary>
+    /// Creates a delegate which will execute the given method and then return
+    /// the result as an object.
+    /// </summary>
+    public static GetValueDelegate<T> CreateUpcastDelegate<T>(MethodInfo method) {
+
+      // The tricky bit is invoking CreateCreateUpcastDelegateImpl with the right type parameters
+      MethodInfo openImpl = typeof(ReflectionUtil).GetMethod("CreateUpcastDelegateImpl");
+      MethodInfo closedImpl = openImpl.MakeGenericMethod(typeof(T), method.ReturnType);
+      return (GetValueDelegate<T>) closedImpl.Invoke(null, new object[] { method });
+    }
+
+    delegate TResult Getter<TSource, TResult>(TSource source);
+
+    /// <summary>
+    /// Method used solely for implementing CreateUpcastDelegate. Public to avoid trust issues
+    /// in low-trust scenarios, e.g. Silverlight.
+    /// TODO(jonskeet): Check any of this actually works in Silverlight...
+    /// </summary>
+    public static GetValueDelegate<TSource> CreateUpcastDelegateImpl<TSource, TResult>(MethodInfo method) {
+      // Convert the reflection call into an open delegate, i.e. instead of calling x.Method()
+      // we'll call getter(x).
+      Getter<TSource, TResult> getter = (Getter<TSource, TResult>)Delegate.CreateDelegate(typeof(Getter<TSource, TResult>), method);
+
+      // Implicit upcast to object (within the delegate)
+      return delegate(TSource source) { return getter(source); };
+    }
+
+
+    /// <summary>
+    /// Creates a delegate which will execute the given method after casting the parameter
+    /// down from object to the required parameter type.
+    /// </summary>
+    public static SingleValueDelegate<T> CreateDowncastDelegate<T>(MethodInfo method) {
+      MethodInfo openImpl = typeof(ReflectionUtil).GetMethod("CreateDowncastDelegateImpl");
+      MethodInfo closedImpl = openImpl.MakeGenericMethod(typeof(T), method.GetParameters()[0].ParameterType);
+      return (SingleValueDelegate<T>)closedImpl.Invoke(null, new object[] { method });
+    }
+
+    delegate void OpenSingleValueDelegate<TSource, TParam>(TSource source, TParam parameter);
+
+    public static SingleValueDelegate<TSource> CreateDowncastDelegateImpl<TSource, TParam>(MethodInfo method) {
+      // Convert the reflection call into an open delegate, i.e. instead of calling x.Method(y) we'll
+      // call Method(x, y)
+      OpenSingleValueDelegate<TSource, TParam> call = (OpenSingleValueDelegate<TSource, TParam>)
+          Delegate.CreateDelegate(typeof(OpenSingleValueDelegate<TSource, TParam>), method);
+
+      return delegate(TSource source, object parameter) { call(source, (TParam)parameter); };
+    }
+
+    /// <summary>
+    /// Creates a delegate which will execute the given method after casting the parameter
+    /// down from object to the required parameter type.
+    /// </summary>
+    public static SingleValueDelegate<T> CreateDowncastDelegateIgnoringReturn<T>(MethodInfo method) {
+      MethodInfo openImpl = typeof(ReflectionUtil).GetMethod("CreateDowncastDelegateIgnoringReturnImpl");
+      MethodInfo closedImpl = openImpl.MakeGenericMethod(typeof(T), method.GetParameters()[0].ParameterType, method.ReturnType);
+      return (SingleValueDelegate<T>)closedImpl.Invoke(null, new object[] { method });
+    }
+
+    delegate TReturn OpenSingleValueDelegate<TSource, TParam, TReturn>(TSource source, TParam parameter);
+
+    public static SingleValueDelegate<TSource> CreateDowncastDelegateIgnoringReturnImpl<TSource, TParam, TReturn>(MethodInfo method) {
+      // Convert the reflection call into an open delegate, i.e. instead of calling x.Method(y) we'll
+      // call Method(x, y)
+      OpenSingleValueDelegate<TSource, TParam, TReturn> call = (OpenSingleValueDelegate<TSource, TParam, TReturn>)
+          Delegate.CreateDelegate(typeof(OpenSingleValueDelegate<TSource, TParam, TReturn>), method);
+
+      return delegate(TSource source, object parameter) { call(source, (TParam)parameter); };
+    }
+
+    delegate T OpenCreateBuilderDelegate<T>();
+
+    /// <summary>
+    /// Creates a delegate which will execute the given static method and cast the result up to IBuilder.
+    /// </summary>
+    public static CreateBuilderDelegate CreateStaticUpcastDelegate(MethodInfo method) {
+      MethodInfo openImpl = typeof(ReflectionUtil).GetMethod("CreateStaticUpcastDelegateImpl");
+      MethodInfo closedImpl = openImpl.MakeGenericMethod(method.ReturnType);
+      return (CreateBuilderDelegate) closedImpl.Invoke(null, new object[] { method });
+    }
+
+    public static CreateBuilderDelegate CreateStaticUpcastDelegateImpl<T>(MethodInfo method) {
+      OpenCreateBuilderDelegate<T> call = (OpenCreateBuilderDelegate<T>)Delegate.CreateDelegate(typeof(OpenCreateBuilderDelegate<T>), method);
+      return delegate { return (IBuilder)call(); };
+    }
+  }
+}