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+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_CALLBACK_H_
+#define BASE_CALLBACK_H_
+
+#include "base/tuple.h"
+#include "base/raw_scoped_refptr_mismatch_checker.h"
+
+// Callback --------------------------------------------------------------------
+//
+// A Callback is like a Task but with unbound parameters. It is basically an
+// object-oriented function pointer.
+//
+// Callbacks are designed to work with Tuples.  A set of helper functions and
+// classes is provided to hide the Tuple details from the consumer.  Client
+// code will generally work with the CallbackRunner base class, which merely
+// provides a Run method and is returned by the New* functions. This allows
+// users to not care which type of class implements the callback, only that it
+// has a certain number and type of arguments.
+//
+// The implementation of this is done by CallbackImpl, which inherits
+// CallbackStorage to store the data. This allows the storage of the data
+// (requiring the class type T) to be hidden from users, who will want to call
+// this regardless of the implementor's type T.
+//
+// Note that callbacks currently have no facility for cancelling or abandoning
+// them. We currently handle this at a higher level for cases where this is
+// necessary. The pointer in a callback must remain valid until the callback
+// is made.
+//
+// Like Task, the callback executor is responsible for deleting the callback
+// pointer once the callback has executed.
+//
+// Example client usage:
+//   void Object::DoStuff(int, string);
+//   Callback2<int, string>::Type* callback =
+//       NewCallback(obj, &Object::DoStuff);
+//   callback->Run(5, string("hello"));
+//   delete callback;
+// or, equivalently, using tuples directly:
+//   CallbackRunner<Tuple2<int, string> >* callback =
+//       NewCallback(obj, &Object::DoStuff);
+//   callback->RunWithParams(MakeTuple(5, string("hello")));
+//
+// There is also a 0-args version that returns a value.  Example:
+//   int Object::GetNextInt();
+//   CallbackWithReturnValue<int>::Type* callback =
+//       NewCallbackWithReturnValue(obj, &Object::GetNextInt);
+//   int next_int = callback->Run();
+//   delete callback;
+
+// Base for all Callbacks that handles storage of the pointers.
+template <class T, typename Method>
+class CallbackStorage {
+ public:
+  CallbackStorage(T* obj, Method meth) : obj_(obj), meth_(meth) {
+  }
+
+ protected:
+  T* obj_;
+  Method meth_;
+};
+
+// Interface that is exposed to the consumer, that does the actual calling
+// of the method.
+template <typename Params>
+class CallbackRunner {
+ public:
+  typedef Params TupleType;
+
+  virtual ~CallbackRunner() {}
+  virtual void RunWithParams(const Params& params) = 0;
+
+  // Convenience functions so callers don't have to deal with Tuples.
+  inline void Run() {
+    RunWithParams(Tuple0());
+  }
+
+  template <typename Arg1>
+  inline void Run(const Arg1& a) {
+    RunWithParams(Params(a));
+  }
+
+  template <typename Arg1, typename Arg2>
+  inline void Run(const Arg1& a, const Arg2& b) {
+    RunWithParams(Params(a, b));
+  }
+
+  template <typename Arg1, typename Arg2, typename Arg3>
+  inline void Run(const Arg1& a, const Arg2& b, const Arg3& c) {
+    RunWithParams(Params(a, b, c));
+  }
+
+  template <typename Arg1, typename Arg2, typename Arg3, typename Arg4>
+  inline void Run(const Arg1& a, const Arg2& b, const Arg3& c, const Arg4& d) {
+    RunWithParams(Params(a, b, c, d));
+  }
+
+  template <typename Arg1, typename Arg2, typename Arg3,
+            typename Arg4, typename Arg5>
+  inline void Run(const Arg1& a, const Arg2& b, const Arg3& c,
+                  const Arg4& d, const Arg5& e) {
+    RunWithParams(Params(a, b, c, d, e));
+  }
+};
+
+template <class T, typename Method, typename Params>
+class CallbackImpl : public CallbackStorage<T, Method>,
+                     public CallbackRunner<Params> {
+ public:
+  CallbackImpl(T* obj, Method meth) : CallbackStorage<T, Method>(obj, meth) {
+  }
+  virtual void RunWithParams(const Params& params) {
+    // use "this->" to force C++ to look inside our templatized base class; see
+    // Effective C++, 3rd Ed, item 43, p210 for details.
+    DispatchToMethod(this->obj_, this->meth_, params);
+  }
+};
+
+// 0-arg implementation
+struct Callback0 {
+  typedef CallbackRunner<Tuple0> Type;
+};
+
+template <class T>
+typename Callback0::Type* NewCallback(T* object, void (T::*method)()) {
+  return new CallbackImpl<T, void (T::*)(), Tuple0 >(object, method);
+}
+
+// 1-arg implementation
+template <typename Arg1>
+struct Callback1 {
+  typedef CallbackRunner<Tuple1<Arg1> > Type;
+};
+
+template <class T, typename Arg1>
+typename Callback1<Arg1>::Type* NewCallback(T* object,
+                                            void (T::*method)(Arg1)) {
+  return new CallbackImpl<T, void (T::*)(Arg1), Tuple1<Arg1> >(object, method);
+}
+
+// 2-arg implementation
+template <typename Arg1, typename Arg2>
+struct Callback2 {
+  typedef CallbackRunner<Tuple2<Arg1, Arg2> > Type;
+};
+
+template <class T, typename Arg1, typename Arg2>
+typename Callback2<Arg1, Arg2>::Type* NewCallback(
+    T* object,
+    void (T::*method)(Arg1, Arg2)) {
+  return new CallbackImpl<T, void (T::*)(Arg1, Arg2),
+      Tuple2<Arg1, Arg2> >(object, method);
+}
+
+// 3-arg implementation
+template <typename Arg1, typename Arg2, typename Arg3>
+struct Callback3 {
+  typedef CallbackRunner<Tuple3<Arg1, Arg2, Arg3> > Type;
+};
+
+template <class T, typename Arg1, typename Arg2, typename Arg3>
+typename Callback3<Arg1, Arg2, Arg3>::Type* NewCallback(
+    T* object,
+    void (T::*method)(Arg1, Arg2, Arg3)) {
+  return new CallbackImpl<T,  void (T::*)(Arg1, Arg2, Arg3),
+      Tuple3<Arg1, Arg2, Arg3> >(object, method);
+}
+
+// 4-arg implementation
+template <typename Arg1, typename Arg2, typename Arg3, typename Arg4>
+struct Callback4 {
+  typedef CallbackRunner<Tuple4<Arg1, Arg2, Arg3, Arg4> > Type;
+};
+
+template <class T, typename Arg1, typename Arg2, typename Arg3, typename Arg4>
+typename Callback4<Arg1, Arg2, Arg3, Arg4>::Type* NewCallback(
+    T* object,
+    void (T::*method)(Arg1, Arg2, Arg3, Arg4)) {
+  return new CallbackImpl<T, void (T::*)(Arg1, Arg2, Arg3, Arg4),
+      Tuple4<Arg1, Arg2, Arg3, Arg4> >(object, method);
+}
+
+// 5-arg implementation
+template <typename Arg1, typename Arg2, typename Arg3,
+          typename Arg4, typename Arg5>
+struct Callback5 {
+  typedef CallbackRunner<Tuple5<Arg1, Arg2, Arg3, Arg4, Arg5> > Type;
+};
+
+template <class T, typename Arg1, typename Arg2,
+          typename Arg3, typename Arg4, typename Arg5>
+typename Callback5<Arg1, Arg2, Arg3, Arg4, Arg5>::Type* NewCallback(
+    T* object,
+    void (T::*method)(Arg1, Arg2, Arg3, Arg4, Arg5)) {
+  return new CallbackImpl<T, void (T::*)(Arg1, Arg2, Arg3, Arg4, Arg5),
+      Tuple5<Arg1, Arg2, Arg3, Arg4, Arg5> >(object, method);
+}
+
+// An UnboundMethod is a wrapper for a method where the actual object is
+// provided at Run dispatch time.
+template <class T, class Method, class Params>
+class UnboundMethod {
+ public:
+  UnboundMethod(Method m, const Params& p) : m_(m), p_(p) {
+    COMPILE_ASSERT((MethodUsesScopedRefptrCorrectly<Method, Params>::value),
+                   badunboundmethodparams);
+  }
+  void Run(T* obj) const {
+    DispatchToMethod(obj, m_, p_);
+  }
+ private:
+  Method m_;
+  Params p_;
+};
+
+// Return value implementation with no args.
+template <typename ReturnValue>
+struct CallbackWithReturnValue {
+  class Type {
+   public:
+    virtual ~Type() {}
+    virtual ReturnValue Run() = 0;
+  };
+};
+
+template <class T, typename Method, typename ReturnValue>
+class CallbackWithReturnValueImpl
+    : public CallbackStorage<T, Method>,
+      public CallbackWithReturnValue<ReturnValue>::Type {
+ public:
+  CallbackWithReturnValueImpl(T* obj, Method meth)
+      : CallbackStorage<T, Method>(obj, meth) {}
+
+  virtual ReturnValue Run() {
+    return (this->obj_->*(this->meth_))();
+  }
+
+ protected:
+  virtual ~CallbackWithReturnValueImpl() {}
+};
+
+template <class T, typename ReturnValue>
+typename CallbackWithReturnValue<ReturnValue>::Type*
+NewCallbackWithReturnValue(T* object, ReturnValue (T::*method)()) {
+  return new CallbackWithReturnValueImpl<T, ReturnValue (T::*)(), ReturnValue>(
+      object, method);
+}
+
+#endif  // BASE_CALLBACK_H