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Diffstat (limited to 'src/ProtocolBuffers/FieldAccess/ReflectionUtil.cs')
-rw-r--r-- | src/ProtocolBuffers/FieldAccess/ReflectionUtil.cs | 109 |
1 files changed, 109 insertions, 0 deletions
diff --git a/src/ProtocolBuffers/FieldAccess/ReflectionUtil.cs b/src/ProtocolBuffers/FieldAccess/ReflectionUtil.cs new file mode 100644 index 00000000..ddec2229 --- /dev/null +++ b/src/ProtocolBuffers/FieldAccess/ReflectionUtil.cs @@ -0,0 +1,109 @@ +// 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 Func<T, object> 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 (Func<T, object>) closedImpl.Invoke(null, new object[] { method }); + } + + /// <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 Func<TSource, object> 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). + Func<TSource, TResult> getter = (Func<TSource, TResult>)Delegate.CreateDelegate(typeof(Func<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 Action<T, object> CreateDowncastDelegate<T>(MethodInfo method) { + MethodInfo openImpl = typeof(ReflectionUtil).GetMethod("CreateDowncastDelegateImpl"); + MethodInfo closedImpl = openImpl.MakeGenericMethod(typeof(T), method.GetParameters()[0].ParameterType); + return (Action<T, object>) closedImpl.Invoke(null, new object[] { method }); + } + + public static Action<TSource, object> 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) + Action<TSource, TParam> call = (Action<TSource, TParam>) Delegate.CreateDelegate(typeof(Action<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 Action<T, object> CreateDowncastDelegateIgnoringReturn<T>(MethodInfo method) { + MethodInfo openImpl = typeof(ReflectionUtil).GetMethod("CreateDowncastDelegateIgnoringReturnImpl"); + MethodInfo closedImpl = openImpl.MakeGenericMethod(typeof(T), method.GetParameters()[0].ParameterType, method.ReturnType); + return (Action<T, object>)closedImpl.Invoke(null, new object[] { method }); + } + + public static Action<TSource, object> 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) + Func<TSource, TParam, TReturn> call = (Func<TSource, TParam, TReturn>) + Delegate.CreateDelegate(typeof(Func<TSource, TParam, TReturn>), method); + + return delegate(TSource source, object parameter) { call(source, (TParam)parameter); }; + } + + /// <summary> + /// Creates a delegate which will execute the given static method and cast the result up to IBuilder. + /// </summary> + public static Func<IBuilder> CreateStaticUpcastDelegate(MethodInfo method) { + MethodInfo openImpl = typeof(ReflectionUtil).GetMethod("CreateStaticUpcastDelegateImpl"); + MethodInfo closedImpl = openImpl.MakeGenericMethod(method.ReturnType); + return (Func<IBuilder>)closedImpl.Invoke(null, new object[] { method }); + } + + public static Func<IBuilder> CreateStaticUpcastDelegateImpl<T>(MethodInfo method) { + Func<T> call = (Func<T>)Delegate.CreateDelegate(typeof(Func<T>), method); + return delegate { return (IBuilder)call(); }; + } + } +} |