Revert of "Redo r113722 - Add Pass(), which implements move semantics, to scoped_ptr, scoped_ar..."

base/bind_helpers.h

Index: base/bind_helpers.h
diff --git a/base/bind_helpers.h b/base/bind_helpers.h
index df8cf82bca5994f41db931999410f0223040642c..6e0f8fe72742a06f7875d5f73a4b9e0ec97f6c45 100644
--- a/base/bind_helpers.h
+++ b/base/bind_helpers.h
@@ -6,29 +6,19 @@
 // can be used specify the refcounting and reference semantics of arguments
 // that are bound by the Bind() function in base/bind.h.
 //
-// The public functions are base::Unretained(), base::Owned(), bass::Passed(),
-// base::ConstRef(), and base::IgnoreResult().
+// The public functions are base::Unretained(), base::Owned(),
+// base::ConstRef(), and base::IgnoreReturn().
 //
 // Unretained() allows Bind() to bind a non-refcounted class, and to disable
 // refcounting on arguments that are refcounted objects.
-//
 // Owned() transfers ownership of an object to the Callback resulting from
 // bind; the object will be deleted when the Callback is deleted.
-//
-// Passed() is for transferring movable-but-not-copyable types (eg. scoped_ptr)
-// through a Callback. Logically, this signifies a destructive transfer of
-// the state of the argument into the target function.  Invoking
-// Callback::Run() twice on a Callback that was created with a Passed()
-// argument will CHECK() because the first invocation would have already
-// transferred ownership to the target function.
-//
 // ConstRef() allows binding a constant reference to an argument rather
 // than a copy.
+// IgnoreReturn() is used to adapt a 0-argument Callback with a return type to
+// a Closure. This is useful if you need to PostTask with a function that has
+// a return value that you don't care about.
 //
-// IgnoreResult() is used to adapt a function or Callback with a return type to
-// one with a void return. This is most useful if you have a function with,
-// say, a pesky ignorable bool return that you want to use with PostTask or
-// something else that expect a Callback with a void return.
 //
 // EXAMPLE OF Unretained():
 //
@@ -85,45 +75,13 @@
 // its bound callbacks.
 //
 //
-// EXAMPLE OF IgnoreResult():
+// EXAMPLE OF IgnoreReturn():
 //
 //   int DoSomething(int arg) { cout << arg << endl; }
-//
-//   // Assign to a Callback with a void return type.
-//   Callback<void(int)> cb = Bind(IgnoreResult(&DoSomething));
-//   cb->Run(1);  // Prints "1".
-//
-//   // Prints "1" on |ml|.
-//   ml->PostTask(FROM_HERE, Bind(IgnoreResult(&DoSomething), 1);
-//
-//
-// EXAMPLE OF Passed():
-//
-//   void TakesOwnership(scoped_ptr<Foo> arg) { }
-//   scoped_ptr<Foo> CreateFoo() { return scoped_ptr<Foo>(new Foo()); }
-//
-//   scoped_ptr<Foo> f(new Foo());
-//
-//   // |cb| is given ownership of Foo(). |f| is now NULL.
-//   // You can use f.Pass() in place of &f, but it's more verbose.
-//   Closure cb = Bind(&TakesOwnership, Passed(&f));
-//
-//   // Run was never called so |cb| still owns Foo() and deletes
-//   // it on Reset().
-//   cb.Reset();
-//
-//   // |cb| is given a new Foo created by CreateFoo().
-//   cb = Bind(&TakesOwnership, Passed(CreateFoo()));
-//
-//   // |arg| in TakesOwnership() is given ownership of Foo(). |cb|
-//   // no longer owns Foo() and, if reset, would not delete Foo().
-//   cb.Run();  // Foo() is now transferred to |arg| and deleted.
-//   cb.Run();  // This CHECK()s since Foo() already been used once.
-//
-// Passed() is particularly useful with PostTask() when you are transferring
-// ownership of an argument into a task, but don't necessarily know if the
-// task will always be executed. This can happen if the task is cancellable
-// or if it is posted to a MessageLoopProxy.
+//   Callback<int(void)> cb = Bind(&DoSomething, 1);
+//   Closure c = IgnoreReturn(cb);  // Prints "1"
+//       or
+//   ml->PostTask(FROM_HERE, IgnoreReturn(cb));  // Prints "1" on |ml|
 
 #ifndef BASE_BIND_HELPERS_H_
 #define BASE_BIND_HELPERS_H_
@@ -329,45 +287,6 @@ class OwnedWrapper {
   mutable T* ptr_;
 };
 
-// PassedWrapper is a copyable adapter for a scoper that ignores const.
-//
-// It is needed to get around the fact that Bind() takes a const reference to
-// all its arguments.  Because Bind() takes a const reference to avoid
-// unnecessary copies, it is incompatible with movable-but-not-copyable
-// types; doing a destructive "move" of the type into Bind() would violate
-// the const correctness.
-//
-// This conundrum cannot be solved without either C++11 rvalue references or
-// a O(2^n) blowup of Bind() templates to handle each combination of regular
-// types and movable-but-not-copyable types.  Thus we introduce a wrapper type
-// that is copyable to transmit the correct type information down into
-// BindState<>. Ignoring const in this type makes sense because it is only
-// created when we are explicitly trying to do a destructive move.
-//
-// Two notes:
-//  1) PassedWrapper supports any type that has a "Pass()" function.
-//     This is intentional. The whitelisting of which specific types we
-//     support is maintained by CallbackParamTraits<>.
-//  2) is_valid_ is distinct from NULL because it is valid to bind a "NULL"
-//     scoper to a Callback and allow the Callback to execute once.
-template <typename T>
-class PassedWrapper {
- public:
-  explicit PassedWrapper(T scoper) : is_valid_(true), scoper_(scoper.Pass()) {}
-  PassedWrapper(const PassedWrapper& other)
-      : is_valid_(other.is_valid_), scoper_(other.scoper_.Pass()) {
-  }
-  T Pass() const {
-    CHECK(is_valid_);
-    is_valid_ = false;
-    return scoper_.Pass();
-  }
-
- private:
-  mutable bool is_valid_;
-  mutable T scoper_;
-};
-
 // Unwrap the stored parameters for the wrappers above.
 template <typename T>
 struct UnwrapTraits {
@@ -411,17 +330,9 @@ struct UnwrapTraits<OwnedWrapper<T> > {
   }
 };
 
-template <typename T>
-struct UnwrapTraits<PassedWrapper<T> > {
-  typedef T ForwardType;
-  static T Unwrap(PassedWrapper<T>& o) {
-    return o.Pass();
-  }
-};
-
 // Utility for handling different refcounting semantics in the Bind()
 // function.
-template <bool is_method, typename T>
+template <bool, typename T>
 struct MaybeRefcount;
 
 template <typename T>
@@ -437,17 +348,23 @@ struct MaybeRefcount<false, T[n]> {
 };
 
 template <typename T>
-struct MaybeRefcount<true, T> {
-  static void AddRef(const T&) {}
-  static void Release(const T&) {}
-};
-
-template <typename T>
 struct MaybeRefcount<true, T*> {
   static void AddRef(T* o) { o->AddRef(); }
   static void Release(T* o) { o->Release(); }
 };
 
+template <typename T>
+struct MaybeRefcount<true, UnretainedWrapper<T> > {
+  static void AddRef(const UnretainedWrapper<T>&) {}
+  static void Release(const UnretainedWrapper<T>&) {}
+};
+
+template <typename T>
+struct MaybeRefcount<true, OwnedWrapper<T> > {
+  static void AddRef(const OwnedWrapper<T>&) {}
+  static void Release(const OwnedWrapper<T>&) {}
+};
+
 // No need to additionally AddRef() and Release() since we are storing a
 // scoped_refptr<> inside the storage object already.
 template <typename T>
@@ -462,13 +379,19 @@ struct MaybeRefcount<true, const T*> {
   static void Release(const T* o) { o->Release(); }
 };
 
+template <typename T>
+struct MaybeRefcount<true, WeakPtr<T> > {
+  static void AddRef(const WeakPtr<T>&) {}
+  static void Release(const WeakPtr<T>&) {}
+};
+
 template <typename R>
 void VoidReturnAdapter(Callback<R(void)> callback) {
   callback.Run();
 }
 
 // IsWeakMethod is a helper that determine if we are binding a WeakPtr<> to a
-// method.  It is used internally by Bind() to select the correct
+// method.  It is unsed internally by Bind() to select the correct
 // InvokeHelper that will no-op itself in the event the WeakPtr<> for
 // the target object is invalidated.
 //
@@ -499,20 +422,6 @@ static inline internal::OwnedWrapper<T> Owned(T* o) {
   return internal::OwnedWrapper<T>(o);
 }
 
-// We offer 2 syntaxes for calling Passed().  The first takes a temporary and
-// is best suited for use with the return value of a function. The second
-// takes a pointer to the scoper and is just syntactic sugar to avoid having
-// to write Passed(scoper.Pass()).
-template <typename T>
-static inline internal::PassedWrapper<T> Passed(T scoper) {
-  return internal::PassedWrapper<T>(scoper.Pass());
-}
-template <typename T>
-static inline internal::PassedWrapper<T> Passed(T* scoper) {
-  return internal::PassedWrapper<T>(scoper->Pass());
-}
-
-// -- DEPRECATED -- Use IgnoreResult instead.
 template <typename R>
 static inline Closure IgnoreReturn(Callback<R(void)> callback) {
   return Bind(&internal::VoidReturnAdapter<R>, callback);
@@ -529,6 +438,7 @@ IgnoreResult(const Callback<T>& data) {
   return internal::IgnoreResultHelper<Callback<T> >(data);
 }
 
+
 }  // namespace base
 
 #endif  // BASE_BIND_HELPERS_H_