Extend base::Callback to have a move-only variant

base/callback_internal.cc

 // 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.
 
 #include "base/callback_internal.h"
 
 #include "base/logging.h"
 
 namespace base {
 namespace internal {
 
 void BindStateBase::AddRef() {
   AtomicRefCountInc(&ref_count_);
 }
 
 void BindStateBase::Release() {
   if (!AtomicRefCountDec(&ref_count_))
     destructor_(this);
 }
 
-CallbackBase::CallbackBase(const CallbackBase& c) = default;
-CallbackBase& CallbackBase::operator=(const CallbackBase& c) = default;
+MoveOnlyCallbackBase::MoveOnlyCallbackBase(MoveOnlyCallbackBase&& c)
+    : bind_state_(std::move(c.bind_state_)),
+      polymorphic_invoke_(c.polymorphic_invoke_) {
+  c.polymorphic_invoke_ = nullptr;
+}
 
-void CallbackBase::Reset() {
-  polymorphic_invoke_ = NULL;
+MoveOnlyCallbackBase& MoveOnlyCallbackBase::operator=(
+    MoveOnlyCallbackBase&& c) {
+  bind_state_ = std::move(c.bind_state_);
+  polymorphic_invoke_ = c.polymorphic_invoke_;
+  c.polymorphic_invoke_ = nullptr;
+  return *this;
+}
+
+void MoveOnlyCallbackBase::Reset() {
+  polymorphic_invoke_ = nullptr;
   // NULL the bind_state_ last, since it may be holding the last ref to whatever
   // object owns us, and we may be deleted after that.
-  bind_state_ = NULL;
+  bind_state_ = nullptr;
 }
 
-bool CallbackBase::Equals(const CallbackBase& other) const {
+bool MoveOnlyCallbackBase::EqualsInternal(
+    const MoveOnlyCallbackBase& other) const {
   return bind_state_.get() == other.bind_state_.get() &&
          polymorphic_invoke_ == other.polymorphic_invoke_;
 }
 
-CallbackBase::CallbackBase(BindStateBase* bind_state)
-    : bind_state_(bind_state),
-      polymorphic_invoke_(NULL) {
+void MoveOnlyCallbackBase::set_bind_state(BindStateBase* bind_state) {
+  bind_state_ = bind_state;
   DCHECK(!bind_state_.get() || bind_state_->ref_count_ == 1);
 }
 
-CallbackBase::~CallbackBase() {
+MoveOnlyCallbackBase::MoveOnlyCallbackBase() {}
+MoveOnlyCallbackBase::~MoveOnlyCallbackBase() {}
+
+CopyableCallbackBase::CopyableCallbackBase(CopyableCallbackBase&& c)
+    : MoveOnlyCallbackBase(std::move(c)) {}
+
+CopyableCallbackBase& CopyableCallbackBase::operator=(
+    CopyableCallbackBase&& c) {
+  *static_cast<MoveOnlyCallbackBase*>(this) = std::move(c);
+  return *this;
+}
+
+CopyableCallbackBase::CopyableCallbackBase(const CopyableCallbackBase& c) {
+  bind_state_ = c.bind_state_;
+  polymorphic_invoke_ = c.polymorphic_invoke_;
+}
+
+CopyableCallbackBase& CopyableCallbackBase::operator=(
+    const CopyableCallbackBase& c) {
+  bind_state_ = c.bind_state_;
+  polymorphic_invoke_ = c.polymorphic_invoke_;
+  return *this;
 }
 
 }  // namespace internal
 }  // namespace base