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

base/callback_internal.cc

Index: base/callback_internal.cc
diff --git a/base/callback_internal.cc b/base/callback_internal.cc
index 2553fe7e1b64bf20c67dde90800377dc44b58fc2..4c8ccae932df1d2e9239903d67fae1745e5b7c1f 100644
--- a/base/callback_internal.cc
+++ b/base/callback_internal.cc
@@ -18,29 +18,66 @@ void BindStateBase::Release() {
     destructor_(this);
 }
 
-CallbackBase::CallbackBase(const CallbackBase& c) = default;
-CallbackBase& CallbackBase::operator=(const CallbackBase& c) = default;
+CallbackBase<CopyMode::MoveOnly>::CallbackBase(CallbackBase&& c)
+    : bind_state_(std::move(c.bind_state_)),
+      polymorphic_invoke_(c.polymorphic_invoke_) {
+  c.polymorphic_invoke_ = nullptr;
+}
+
+CallbackBase<CopyMode::MoveOnly>&
+CallbackBase<CopyMode::MoveOnly>::operator=(CallbackBase&& c) {
+  bind_state_ = std::move(c.bind_state_);
+  polymorphic_invoke_ = c.polymorphic_invoke_;
+  c.polymorphic_invoke_ = nullptr;
+  return *this;
+}
 
-void CallbackBase::Reset() {
-  polymorphic_invoke_ = NULL;
+void CallbackBase<CopyMode::MoveOnly>::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 CallbackBase<CopyMode::MoveOnly>::EqualsInternal(
+    const CallbackBase& 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) {
+CallbackBase<CopyMode::MoveOnly>::CallbackBase(
+    BindStateBase* bind_state)
+    : bind_state_(bind_state) {
   DCHECK(!bind_state_.get() || bind_state_->ref_count_ == 1);
 }
 
-CallbackBase::~CallbackBase() {
+CallbackBase<CopyMode::MoveOnly>::~CallbackBase() {}
+
+CallbackBase<CopyMode::Copyable>::CallbackBase(
+    const CallbackBase& c)
+    : CallbackBase<CopyMode::MoveOnly>(nullptr) {
+  bind_state_ = c.bind_state_;
+  polymorphic_invoke_ = c.polymorphic_invoke_;
+}
+
+CallbackBase<CopyMode::Copyable>::CallbackBase(CallbackBase&& c)
+    : CallbackBase<CopyMode::MoveOnly>(std::move(c)) {}
+
+CallbackBase<CopyMode::Copyable>&
+CallbackBase<CopyMode::Copyable>::operator=(const CallbackBase& c) {
+  bind_state_ = c.bind_state_;
+  polymorphic_invoke_ = c.polymorphic_invoke_;
+  return *this;
 }
 
+CallbackBase<CopyMode::Copyable>&
+CallbackBase<CopyMode::Copyable>::operator=(CallbackBase&& c) {
+  *static_cast<CallbackBase<CopyMode::MoveOnly>*>(this) = std::move(c);
+  return *this;
+}
+
+template class CallbackBase<CopyMode::MoveOnly>;
+template class CallbackBase<CopyMode::Copyable>;
+
 }  // namespace internal
 }  // namespace base