// 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 {
///
/// 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.
///
internal static class ReflectionUtil {
///
/// Creates a delegate which will execute the given method and then return
/// the result as an object.
///
public static Func CreateUpcastDelegate(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) closedImpl.Invoke(null, new object[] { method });
}
///
/// 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...
///
public static Func CreateUpcastDelegateImpl(MethodInfo method) {
// Convert the reflection call into an open delegate, i.e. instead of calling x.Method()
// we'll call getter(x).
Func getter = (Func)Delegate.CreateDelegate(typeof(Func), method);
// Implicit upcast to object (within the delegate)
return delegate(TSource source) { return getter(source); };
}
///
/// Creates a delegate which will execute the given method after casting the parameter
/// down from object to the required parameter type.
///
public static Action CreateDowncastDelegate(MethodInfo method) {
MethodInfo openImpl = typeof(ReflectionUtil).GetMethod("CreateDowncastDelegateImpl");
MethodInfo closedImpl = openImpl.MakeGenericMethod(typeof(T), method.GetParameters()[0].ParameterType);
return (Action) closedImpl.Invoke(null, new object[] { method });
}
public static Action CreateDowncastDelegateImpl(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 call = (Action) Delegate.CreateDelegate(typeof(Action), method);
return delegate(TSource source, object parameter) { call(source, (TParam)parameter); };
}
///
/// Creates a delegate which will execute the given method after casting the parameter
/// down from object to the required parameter type.
///
public static Action CreateDowncastDelegateIgnoringReturn(MethodInfo method) {
MethodInfo openImpl = typeof(ReflectionUtil).GetMethod("CreateDowncastDelegateIgnoringReturnImpl");
MethodInfo closedImpl = openImpl.MakeGenericMethod(typeof(T), method.GetParameters()[0].ParameterType, method.ReturnType);
return (Action)closedImpl.Invoke(null, new object[] { method });
}
public static Action CreateDowncastDelegateIgnoringReturnImpl(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 call = (Func)
Delegate.CreateDelegate(typeof(Func), method);
return delegate(TSource source, object parameter) { call(source, (TParam)parameter); };
}
///
/// Creates a delegate which will execute the given static method and cast the result up to IBuilder.
///
public static Func CreateStaticUpcastDelegate(MethodInfo method) {
MethodInfo openImpl = typeof(ReflectionUtil).GetMethod("CreateStaticUpcastDelegateImpl");
MethodInfo closedImpl = openImpl.MakeGenericMethod(method.ReturnType);
return (Func)closedImpl.Invoke(null, new object[] { method });
}
public static Func CreateStaticUpcastDelegateImpl(MethodInfo method) {
Func call = (Func)Delegate.CreateDelegate(typeof(Func), method);
return delegate { return (IBuilder)call(); };
}
}
}