text: // This file was GENERATED by command:
  //     pump.py callback.h.pump
  // DO NOT EDIT BY HAND!!!
  
  
  // Copyright (c) 2012 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 "callback_forward.h"
  #include "callback_internal.h"
  #include "template_util.h"
  
  // NOTE: Header files that do not require the full definition of Callback or
  // Closure should #include "base/callback_forward.h" instead of this file.
  
  // -----------------------------------------------------------------------------
  // Introduction
  // -----------------------------------------------------------------------------
  //
  // The templated Callback class is a generalized function object. Together
  // with the Bind() function in bind.h, they provide a type-safe method for
  // performing partial application of functions.
  //
  // Partial application (or "currying") is the process of binding a subset of
  // a function's arguments to produce another function that takes fewer
  // arguments. This can be used to pass around a unit of delayed execution,
  // much like lexical closures are used in other languages. For example, it
  // is used in Chromium code to schedule tasks on different MessageLoops.
  //
  // A callback with no unbound input parameters (base::Callback<void(void)>)
  // is called a base::Closure. Note that this is NOT the same as what other
  // languages refer to as a closure -- it does not retain a reference to its
  // enclosing environment.
  //
  // MEMORY MANAGEMENT AND PASSING
  //
  // The Callback objects themselves should be passed by const-reference, and
  // stored by copy. They internally store their state via a refcounted class
  // and thus do not need to be deleted.
  //
  // The reason to pass via a const-reference is to avoid unnecessary
  // AddRef/Release pairs to the internal state.
  //
  //
  // -----------------------------------------------------------------------------
  // Quick reference for basic stuff
  // -----------------------------------------------------------------------------
  //
  // BINDING A BARE FUNCTION
  //
  //   int Return5() { return 5; }
  //   base::Callback<int(void)> func_cb = base::Bind(&Return5);
  //   LOG(INFO) << func_cb.Run();  // Prints 5.
  //
  // BINDING A CLASS METHOD
  //
  //   The first argument to bind is the member function to call, the second is
  //   the object on which to call it.
  //
  //   class Ref : public base::RefCountedThreadSafe<Ref> {
  //    public:
  //     int Foo() { return 3; }
  //     void PrintBye() { LOG(INFO) << "bye."; }
  //   };
  //   scoped_refptr<Ref> ref = new Ref();
  //   base::Callback<void(void)> ref_cb = base::Bind(&Ref::Foo, ref);
  //   LOG(INFO) << ref_cb.Run();  // Prints out 3.
  //
  //   By default the object must support RefCounted or you will get a compiler
  //   error. If you're passing between threads, be sure it's
  //   RefCountedThreadSafe! See "Advanced binding of member functions" below if
  //   you don't want to use reference counting.
  //
  // RUNNING A CALLBACK
  //
  //   Callbacks can be run with their "Run" method, which has the same
  //   signature as the template argument to the callback.
  //
  //   void DoSomething(const base::Callback<void(int, std::string)>& callback) {
  //     callback.Run(5, "hello");
  //   }
  //
  //   Callbacks can be run more than once (they don't get deleted or marked when
  //   run). However, this precludes using base::Passed (see below).
  //
  //   void DoSomething(const base::Callback<double(double)>& callback) {
  //     double myresult = callback.Run(3.14159);
  //     myresult += callback.Run(2.71828);
  //   }
  //
  // PASSING UNBOUND INPUT PARAMETERS
  //
  //   Unbound parameters are specified at the time a callback is Run(). They are
  //   specified in the Callback template type:
  //
  //   void MyFunc(int i, const std::string& str) {}
  //   base::Callback<void(int, const std::string&)> cb = base::Bind(&MyFunc);
  //   cb.Run(23, "hello, world");
  //
  // PASSING BOUND INPUT PARAMETERS
  //
  //   Bound parameters are specified when you create thee callback as arguments
  //   to Bind(). They will be passed to the function and the Run()ner of the
  //   callback doesn't see those values or even know that the function it's
  //   calling.
  //
  //   void MyFunc(int i, const std::string& str) {}
  //   base::Callback<void(void)> cb = base::Bind(&MyFunc, 23, "hello world");
  //   cb.Run();
  //
  //   A callback with no unbound input parameters (base::Callback<void(void)>)
  //   is called a base::Closure. So we could have also written:
  //
  //   base::Closure cb = base::Bind(&MyFunc, 23, "hello world");
  //
  //   When calling member functions, bound parameters just go after the object
  //   pointer.
  //
  //   base::Closure cb = base::Bind(&MyClass::MyFunc, this, 23, "hello world");
  //
  // PARTIAL BINDING OF PARAMETERS
  //
  //   You can specify some parameters when you create the callback, and specify
  //   the rest when you execute the callback.
  //
  //   void MyFunc(int i, const std::string& str) {}
  //   base::Callback<void(const std::string&)> cb = base::Bind(&MyFunc, 23);
  //   cb.Run("hello world");
  //
  //   When calling a function bound parameters are first, followed by unbound
  //   parameters.
  //
  //
  // -----------------------------------------------------------------------------
  // Quick reference for advanced binding
  // -----------------------------------------------------------------------------
  //
  // BINDING A CLASS METHOD WITH WEAK POINTERS
  //
  //   base::Bind(&MyClass::Foo, GetWeakPtr());
  //
  //   The callback will not be issued if the object is destroyed at the time
  //   it's issued. DANGER: weak pointers are not threadsafe, so don't use this
  //   when passing between threads!
  //
  // BINDING A CLASS METHOD WITH MANUAL LIFETIME MANAGEMENT
  //
  //   base::Bind(&MyClass::Foo, base::Unretained(this));
  //
  //   This disables all lifetime management on the object. You're responsible
  //   for making sure the object is alive at the time of the call. You break it,
  //   you own it!
  //
  // BINDING A CLASS METHOD AND HAVING THE CALLBACK OWN THE CLASS
  //
  //   MyClass* myclass = new MyClass;
  //   base::Bind(&MyClass::Foo, base::Owned(myclass));
  //
  //   The object will be deleted when the callback is destroyed, even if it's
  //   not run (like if you post a task during shutdown). Potentially useful for
  //   "fire and forget" cases.
  //
  // IGNORING RETURN VALUES
  //
  //   Sometimes you want to call a function that returns a value in a callback
  //   that doesn't expect a return value.
  //
  //   int DoSomething(int arg) { cout << arg << endl; }
  //   base::Callback<void<int>) cb =
  //       base::Bind(base::IgnoreResult(&DoSomething));
  //
  //
  // -----------------------------------------------------------------------------
  // Quick reference for binding parameters to Bind()
  // -----------------------------------------------------------------------------
  //
  // Bound parameters are specified as arguments to Bind() and are passed to the
  // function. A callback with no parameters or no unbound parameters is called a
  // Closure (base::Callback<void(void)> and base::Closure are the same thing).
  //
  // PASSING PARAMETERS OWNED BY THE CALLBACK
  //
  //   void Foo(int* arg) { cout << *arg << endl; }
  //   int* pn = new int(1);
  //   base::Closure foo_callback = base::Bind(&foo, base::Owned(pn));
  //
  //   The parameter will be deleted when the callback is destroyed, even if it's
  //   not run (like if you post a task during shutdown).
  //
  // PASSING PARAMETERS AS A scoped_ptr
  //
  //   void TakesOwnership(scoped_ptr<Foo> arg) {}
  //   scoped_ptr<Foo> f(new Foo);
  //   // f becomes null during the following call.
  //   base::Closure cb = base::Bind(&TakesOwnership, base::Passed(&f));
  //
  //   Ownership of the parameter will be with the callback until the it is run,
  //   when ownership is passed to the callback function. This means the callback
  //   can only be run once. If the callback is never run, it will delete the
  //   object when it's destroyed.
  //
  // PASSING PARAMETERS AS A scoped_refptr
  //
  //   void TakesOneRef(scoped_refptr<Foo> arg) {}
  //   scoped_refptr<Foo> f(new Foo)
  //   base::Closure cb = base::Bind(&TakesOneRef, f);
  //
  //   This should "just work." The closure will take a reference as long as it
  //   is alive, and another reference will be taken for the called function.
  //
  // PASSING PARAMETERS BY REFERENCE
  //
  //   Const references are *copied* unless ConstRef is used. Example:
  //
  //   void foo(const int& arg) { printf("%d %p\n", arg, &arg); }
  //   int n = 1;
  //   base::Closure has_copy = base::Bind(&foo, n);
  //   base::Closure has_ref = base::Bind(&foo, base::ConstRef(n));
  //   n = 2;
  //   foo(n);                        // Prints "2 0xaaaaaaaaaaaa"
  //   has_copy.Run();                // Prints "1 0xbbbbbbbbbbbb"
  //   has_ref.Run();                 // Prints "2 0xaaaaaaaaaaaa"
  //
  //   Normally parameters are copied in the closure. DANGER: ConstRef stores a
  //   const reference instead, referencing the original parameter. This means
  //   that you must ensure the object outlives the callback!
  //
  //
  // -----------------------------------------------------------------------------
  // Implementation notes
  // -----------------------------------------------------------------------------
  //
  // WHERE IS THIS DESIGN FROM:
  //
  // The design Callback and Bind is heavily influenced by C++'s
  // tr1::function/tr1::bind, and by the "Google Callback" system used inside
  // Google.
  //
  //
  // HOW THE IMPLEMENTATION WORKS:
  //
  // There are three main components to the system:
  //   1) The Callback classes.
  //   2) The Bind() functions.
  //   3) The arguments wrappers (e.g., Unretained() and ConstRef()).
  //
  // The Callback classes represent a generic function pointer. Internally,
  // it stores a refcounted piece of state that represents the target function
  // and all its bound parameters.  Each Callback specialization has a templated
  // constructor that takes an BindState<>*.  In the context of the constructor,
  // the static type of this BindState<> pointer uniquely identifies the
  // function it is representing, all its bound parameters, and a Run() method
  // that is capable of invoking the target.
  //
  // Callback's constructor takes the BindState<>* that has the full static type
  // and erases the target function type as well as the types of the bound
  // parameters.  It does this by storing a pointer to the specific Run()
  // function, and upcasting the state of BindState<>* to a
  // BindStateBase*. This is safe as long as this BindStateBase pointer
  // is only used with the stored Run() pointer.
  //
  // To BindState<> objects are created inside the Bind() functions.
  // These functions, along with a set of internal templates, are responsible for
  //
  //  - Unwrapping the function signature into return type, and parameters
  //  - Determining the number of parameters that are bound
  //  - Creating the BindState storing the bound parameters
  //  - Performing compile-time asserts to avoid error-prone behavior
  //  - Returning an Callback<> with an arity matching the number of unbound
  //    parameters and that knows the correct refcounting semantics for the
  //    target object if we are binding a method.
  //
  // The Bind functions do the above using type-inference, and template
  // specializations.
  //
  // By default Bind() will store copies of all bound parameters, and attempt
  // to refcount a target object if the function being bound is a class method.
  // These copies are created even if the function takes parameters as const
  // references. (Binding to non-const references is forbidden, see bind.h.)
  //
  // To change this behavior, we introduce a set of argument wrappers
  // (e.g., Unretained(), and ConstRef()).  These are simple container templates
  // that are passed by value, and wrap a pointer to argument.  See the
  // file-level comment in base/bind_helpers.h for more info.
  //
  // These types are passed to the Unwrap() functions, and the MaybeRefcount()
  // functions respectively to modify the behavior of Bind().  The Unwrap()
  // and MaybeRefcount() functions change behavior by doing partial
  // specialization based on whether or not a parameter is a wrapper type.
  //
  // ConstRef() is similar to tr1::cref.  Unretained() is specific to Chromium.
  //
  //
  // WHY NOT TR1 FUNCTION/BIND?
  //
  // Direct use of tr1::function and tr1::bind was considered, but ultimately
  // rejected because of the number of copy constructors invocations involved
  // in the binding of arguments during construction, and the forwarding of
  // arguments during invocation.  These copies will no longer be an issue in
  // C++0x because C++0x will support rvalue reference allowing for the compiler
  // to avoid these copies.  However, waiting for C++0x is not an option.
  //
  // Measured with valgrind on gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5), the
  // tr1::bind call itself will invoke a non-trivial copy constructor three times
  // for each bound parameter.  Also, each when passing a tr1::function, each
  // bound argument will be copied again.
  //
  // In addition to the copies taken at binding and invocation, copying a
  // tr1::function causes a copy to be made of all the bound parameters and
  // state.
  //
  // Furthermore, in Chromium, it is desirable for the Callback to take a
  // reference on a target object when representing a class method call.  This
  // is not supported by tr1.
  //
  // Lastly, tr1::function and tr1::bind has a more general and flexible API.
  // This includes things like argument reordering by use of
  // tr1::bind::placeholder, support for non-const reference parameters, and some
  // limited amount of subtyping of the tr1::function object (e.g.,
  // tr1::function<int(int)> is convertible to tr1::function<void(int)>).
  //
  // These are not features that are required in Chromium. Some of them, such as
  // allowing for reference parameters, and subtyping of functions, may actually
  // become a source of errors. Removing support for these features actually
  // allows for a simpler implementation, and a terser Currying API.
  //
  //
  // WHY NOT GOOGLE CALLBACKS?
  //
  // The Google callback system also does not support refcounting.  Furthermore,
  // its implementation has a number of strange edge cases with respect to type
  // conversion of its arguments.  In particular, the argument's constness must
  // at times match exactly the function signature, or the type-inference might
  // break.  Given the above, writing a custom solution was easier.
  //
  //
  // MISSING FUNCTIONALITY
  //  - Invoking the return of Bind.  Bind(&foo).Run() does not work;
  //  - Binding arrays to functions that take a non-const pointer.
  //    Example:
  //      void Foo(const char* ptr);
  //      void Bar(char* ptr);
  //      Bind(&Foo, "test");
  //      Bind(&Bar, "test");  // This fails because ptr is not const.
  
  namespace base {
  
  // First, we forward declare the Callback class template. This informs the
  // compiler that the template only has 1 type parameter which is the function
  // signature that the Callback is representing.
  //
  // After this, create template specializations for 0-7 parameters. Note that
  // even though the template typelist grows, the specialization still
  // only has one type: the function signature.
  //
  // If you are thinking of forward declaring Callback in your own header file,
  // please include "base/callback_forward.h" instead.
  template <typename Sig>
  class Callback;
  
  namespace internal {
  template <typename Runnable, typename RunType, typename BoundArgsType>
  struct BindState;
  }  // namespace internal
  
  template <typename R>
  class Callback<R(void)> : public internal::CallbackBase {
   public:
    typedef R(RunType)();
  
    Callback() : CallbackBase(NULL) { }
  
    // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
    // return the exact Callback<> type.  See base/bind.h for details.
    template <typename Runnable, typename BindRunType, typename BoundArgsType>
    Callback(internal::BindState<Runnable, BindRunType,
             BoundArgsType>* bind_state)
        : CallbackBase(bind_state) {
  
      // Force the assignment to a local variable of PolymorphicInvoke
      // so the compiler will typecheck that the passed in Run() method has
      // the correct type.
      PolymorphicInvoke invoke_func =
          &internal::BindState<Runnable, BindRunType, BoundArgsType>
              ::InvokerType::Run;
      polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
    }
  
    bool Equals(const Callback& other) const {
      return CallbackBase::Equals(other);
    }
  
    R Run() const {
      PolymorphicInvoke f =
          reinterpret_cast<PolymorphicInvoke>(polymorphic_invoke_);
  
      return f(bind_state_.get());
    }
  
   private:
    typedef R(*PolymorphicInvoke)(
        internal::BindStateBase*);
  
  };
  
  template <typename R, typename A1>
  class Callback<R(A1)> : public internal::CallbackBase {
   public:
    typedef R(RunType)(A1);
  
    Callback() : CallbackBase(NULL) { }
  
    // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
    // return the exact Callback<> type.  See base/bind.h for details.
    template <typename Runnable, typename BindRunType, typename BoundArgsType>
    Callback(internal::BindState<Runnable, BindRunType,
             BoundArgsType>* bind_state)
        : CallbackBase(bind_state) {
  
      // Force the assignment to a local variable of PolymorphicInvoke
      // so the compiler will typecheck that the passed in Run() method has
      // the correct type.
      PolymorphicInvoke invoke_func =
          &internal::BindState<Runnable, BindRunType, BoundArgsType>
              ::InvokerType::Run;
      polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
    }
  
    bool Equals(const Callback& other) const {
      return CallbackBase::Equals(other);
    }
  
    R Run(typename internal::CallbackParamTraits<A1>::ForwardType a1) const {
      PolymorphicInvoke f =
          reinterpret_cast<PolymorphicInvoke>(polymorphic_invoke_);
  
      return f(bind_state_.get(), internal::CallbackForward(a1));
    }
  
   private:
    typedef R(*PolymorphicInvoke)(
        internal::BindStateBase*,
            typename internal::CallbackParamTraits<A1>::ForwardType);
  
  };
  
  template <typename R, typename A1, typename A2>
  class Callback<R(A1, A2)> : public internal::CallbackBase {
   public:
    typedef R(RunType)(A1, A2);
  
    Callback() : CallbackBase(NULL) { }
  
    // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
    // return the exact Callback<> type.  See base/bind.h for details.
    template <typename Runnable, typename BindRunType, typename BoundArgsType>
    Callback(internal::BindState<Runnable, BindRunType,
             BoundArgsType>* bind_state)
        : CallbackBase(bind_state) {
  
      // Force the assignment to a local variable of PolymorphicInvoke
      // so the compiler will typecheck that the passed in Run() method has
      // the correct type.
      PolymorphicInvoke invoke_func =
          &internal::BindState<Runnable, BindRunType, BoundArgsType>
              ::InvokerType::Run;
      polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
    }
  
    bool Equals(const Callback& other) const {
      return CallbackBase::Equals(other);
    }
  
    R Run(typename internal::CallbackParamTraits<A1>::ForwardType a1,
          typename internal::CallbackParamTraits<A2>::ForwardType a2) const {
      PolymorphicInvoke f =
          reinterpret_cast<PolymorphicInvoke>(polymorphic_invoke_);
  
      return f(bind_state_.get(), internal::CallbackForward(a1),
               internal::CallbackForward(a2));
    }
  
   private:
    typedef R(*PolymorphicInvoke)(
        internal::BindStateBase*,
            typename internal::CallbackParamTraits<A1>::ForwardType,
            typename internal::CallbackParamTraits<A2>::ForwardType);
  
  };
  
  template <typename R, typename A1, typename A2, typename A3>
  class Callback<R(A1, A2, A3)> : public internal::CallbackBase {
   public:
    typedef R(RunType)(A1, A2, A3);
  
    Callback() : CallbackBase(NULL) { }
  
    // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
    // return the exact Callback<> type.  See base/bind.h for details.
    template <typename Runnable, typename BindRunType, typename BoundArgsType>
    Callback(internal::BindState<Runnable, BindRunType,
             BoundArgsType>* bind_state)
        : CallbackBase(bind_state) {
  
      // Force the assignment to a local variable of PolymorphicInvoke
      // so the compiler will typecheck that the passed in Run() method has
      // the correct type.
      PolymorphicInvoke invoke_func =
          &internal::BindState<Runnable, BindRunType, BoundArgsType>
              ::InvokerType::Run;
      polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
    }
  
    bool Equals(const Callback& other) const {
      return CallbackBase::Equals(other);
    }
  
    R Run(typename internal::CallbackParamTraits<A1>::ForwardType a1,
          typename internal::CallbackParamTraits<A2>::ForwardType a2,
          typename internal::CallbackParamTraits<A3>::ForwardType a3) const {
      PolymorphicInvoke f =
          reinterpret_cast<PolymorphicInvoke>(polymorphic_invoke_);
  
      return f(bind_state_.get(), internal::CallbackForward(a1),
               internal::CallbackForward(a2),
               internal::CallbackForward(a3));
    }
  
   private:
    typedef R(*PolymorphicInvoke)(
        internal::BindStateBase*,
            typename internal::CallbackParamTraits<A1>::ForwardType,
            typename internal::CallbackParamTraits<A2>::ForwardType,
            typename internal::CallbackParamTraits<A3>::ForwardType);
  
  };
  
  template <typename R, typename A1, typename A2, typename A3, typename A4>
  class Callback<R(A1, A2, A3, A4)> : public internal::CallbackBase {
   public:
    typedef R(RunType)(A1, A2, A3, A4);
  
    Callback() : CallbackBase(NULL) { }
  
    // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
    // return the exact Callback<> type.  See base/bind.h for details.
    template <typename Runnable, typename BindRunType, typename BoundArgsType>
    Callback(internal::BindState<Runnable, BindRunType,
             BoundArgsType>* bind_state)
        : CallbackBase(bind_state) {
  
      // Force the assignment to a local variable of PolymorphicInvoke
      // so the compiler will typecheck that the passed in Run() method has
      // the correct type.
      PolymorphicInvoke invoke_func =
          &internal::BindState<Runnable, BindRunType, BoundArgsType>
              ::InvokerType::Run;
      polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
    }
  
    bool Equals(const Callback& other) const {
      return CallbackBase::Equals(other);
    }
  
    R Run(typename internal::CallbackParamTraits<A1>::ForwardType a1,
          typename internal::CallbackParamTraits<A2>::ForwardType a2,
          typename internal::CallbackParamTraits<A3>::ForwardType a3,
          typename internal::CallbackParamTraits<A4>::ForwardType a4) const {
      PolymorphicInvoke f =
          reinterpret_cast<PolymorphicInvoke>(polymorphic_invoke_);
  
      return f(bind_state_.get(), internal::CallbackForward(a1),
               internal::CallbackForward(a2),
               internal::CallbackForward(a3),
               internal::CallbackForward(a4));
    }
  
   private:
    typedef R(*PolymorphicInvoke)(
        internal::BindStateBase*,
            typename internal::CallbackParamTraits<A1>::ForwardType,
            typename internal::CallbackParamTraits<A2>::ForwardType,
            typename internal::CallbackParamTraits<A3>::ForwardType,
            typename internal::CallbackParamTraits<A4>::ForwardType);
  
  };
  
  template <typename R, typename A1, typename A2, typename A3, typename A4,
      typename A5>
  class Callback<R(A1, A2, A3, A4, A5)> : public internal::CallbackBase {
   public:
    typedef R(RunType)(A1, A2, A3, A4, A5);
  
    Callback() : CallbackBase(NULL) { }
  
    // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
    // return the exact Callback<> type.  See base/bind.h for details.
    template <typename Runnable, typename BindRunType, typename BoundArgsType>
    Callback(internal::BindState<Runnable, BindRunType,
             BoundArgsType>* bind_state)
        : CallbackBase(bind_state) {
  
      // Force the assignment to a local variable of PolymorphicInvoke
      // so the compiler will typecheck that the passed in Run() method has
      // the correct type.
      PolymorphicInvoke invoke_func =
          &internal::BindState<Runnable, BindRunType, BoundArgsType>
              ::InvokerType::Run;
      polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
    }
  
    bool Equals(const Callback& other) const {
      return CallbackBase::Equals(other);
    }
  
    R Run(typename internal::CallbackParamTraits<A1>::ForwardType a1,
          typename internal::CallbackParamTraits<A2>::ForwardType a2,
          typename internal::CallbackParamTraits<A3>::ForwardType a3,
          typename internal::CallbackParamTraits<A4>::ForwardType a4,
          typename internal::CallbackParamTraits<A5>::ForwardType a5) const {
      PolymorphicInvoke f =
          reinterpret_cast<PolymorphicInvoke>(polymorphic_invoke_);
  
      return f(bind_state_.get(), internal::CallbackForward(a1),
               internal::CallbackForward(a2),
               internal::CallbackForward(a3),
               internal::CallbackForward(a4),
               internal::CallbackForward(a5));
    }
  
   private:
    typedef R(*PolymorphicInvoke)(
        internal::BindStateBase*,
            typename internal::CallbackParamTraits<A1>::ForwardType,
            typename internal::CallbackParamTraits<A2>::ForwardType,
            typename internal::CallbackParamTraits<A3>::ForwardType,
            typename internal::CallbackParamTraits<A4>::ForwardType,
            typename internal::CallbackParamTraits<A5>::ForwardType);
  
  };
  
  template <typename R, typename A1, typename A2, typename A3, typename A4,
      typename A5, typename A6>
  class Callback<R(A1, A2, A3, A4, A5, A6)> : public internal::CallbackBase {
   public:
    typedef R(RunType)(A1, A2, A3, A4, A5, A6);
  
    Callback() : CallbackBase(NULL) { }
  
    // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
    // return the exact Callback<> type.  See base/bind.h for details.
    template <typename Runnable, typename BindRunType, typename BoundArgsType>
    Callback(internal::BindState<Runnable, BindRunType,
             BoundArgsType>* bind_state)
        : CallbackBase(bind_state) {
  
      // Force the assignment to a local variable of PolymorphicInvoke
      // so the compiler will typecheck that the passed in Run() method has
      // the correct type.
      PolymorphicInvoke invoke_func =
          &internal::BindState<Runnable, BindRunType, BoundArgsType>
              ::InvokerType::Run;
      polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
    }
  
    bool Equals(const Callback& other) const {
      return CallbackBase::Equals(other);
    }
  
    R Run(typename internal::CallbackParamTraits<A1>::ForwardType a1,
          typename internal::CallbackParamTraits<A2>::ForwardType a2,
          typename internal::CallbackParamTraits<A3>::ForwardType a3,
          typename internal::CallbackParamTraits<A4>::ForwardType a4,
          typename internal::CallbackParamTraits<A5>::ForwardType a5,
          typename internal::CallbackParamTraits<A6>::ForwardType a6) const {
      PolymorphicInvoke f =
          reinterpret_cast<PolymorphicInvoke>(polymorphic_invoke_);
  
      return f(bind_state_.get(), internal::CallbackForward(a1),
               internal::CallbackForward(a2),
               internal::CallbackForward(a3),
               internal::CallbackForward(a4),
               internal::CallbackForward(a5),
               internal::CallbackForward(a6));
    }
  
   private:
    typedef R(*PolymorphicInvoke)(
        internal::BindStateBase*,
            typename internal::CallbackParamTraits<A1>::ForwardType,
            typename internal::CallbackParamTraits<A2>::ForwardType,
            typename internal::CallbackParamTraits<A3>::ForwardType,
            typename internal::CallbackParamTraits<A4>::ForwardType,
            typename internal::CallbackParamTraits<A5>::ForwardType,
            typename internal::CallbackParamTraits<A6>::ForwardType);
  
  };
  
  template <typename R, typename A1, typename A2, typename A3, typename A4,
      typename A5, typename A6, typename A7>
  class Callback<R(A1, A2, A3, A4, A5, A6, A7)> : public internal::CallbackBase {
   public:
    typedef R(RunType)(A1, A2, A3, A4, A5, A6, A7);
  
    Callback() : CallbackBase(NULL) { }
  
    // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
    // return the exact Callback<> type.  See base/bind.h for details.
    template <typename Runnable, typename BindRunType, typename BoundArgsType>
    Callback(internal::BindState<Runnable, BindRunType,
             BoundArgsType>* bind_state)
        : CallbackBase(bind_state) {
  
      // Force the assignment to a local variable of PolymorphicInvoke
      // so the compiler will typecheck that the passed in Run() method has
      // the correct type.
      PolymorphicInvoke invoke_func =
          &internal::BindState<Runnable, BindRunType, BoundArgsType>
              ::InvokerType::Run;
      polymorphic_invoke_ = reinterpret_cast<InvokeFuncStorage>(invoke_func);
    }
  
    bool Equals(const Callback& other) const {
      return CallbackBase::Equals(other);
    }
  
    R Run(typename internal::CallbackParamTraits<A1>::ForwardType a1,
          typename internal::CallbackParamTraits<A2>::ForwardType a2,
          typename internal::CallbackParamTraits<A3>::ForwardType a3,
          typename internal::CallbackParamTraits<A4>::ForwardType a4,
          typename internal::CallbackParamTraits<A5>::ForwardType a5,
          typename internal::CallbackParamTraits<A6>::ForwardType a6,
          typename internal::CallbackParamTraits<A7>::ForwardType a7) const {
      PolymorphicInvoke f =
          reinterpret_cast<PolymorphicInvoke>(polymorphic_invoke_);
  
      return f(bind_state_.get(), internal::CallbackForward(a1),
               internal::CallbackForward(a2),
               internal::CallbackForward(a3),
               internal::CallbackForward(a4),
               internal::CallbackForward(a5),
               internal::CallbackForward(a6),
               internal::CallbackForward(a7));
    }
  
   private:
    typedef R(*PolymorphicInvoke)(
        internal::BindStateBase*,
            typename internal::CallbackParamTraits<A1>::ForwardType,
            typename internal::CallbackParamTraits<A2>::ForwardType,
            typename internal::CallbackParamTraits<A3>::ForwardType,
            typename internal::CallbackParamTraits<A4>::ForwardType,
            typename internal::CallbackParamTraits<A5>::ForwardType,
            typename internal::CallbackParamTraits<A6>::ForwardType,
            typename internal::CallbackParamTraits<A7>::ForwardType);
  
  };
  
  
  // Syntactic sugar to make Callbacks<void(void)> easier to declare since it
  // will be used in a lot of APIs with delayed execution.
  typedef Callback<void(void)> Closure;
  
  }  // namespace base
  
  #endif  // BASE_CALLBACK_H
  