Add nullptr support to scoped_ptr.

base/memory/scoped_ptr.h

 // 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.
 
 // Scopers help you manage ownership of a pointer, helping you easily manage a
 // pointer within a scope, and automatically destroying the pointer at the end
 // of a scope.  There are two main classes you will use, which correspond to the
 // operators new/delete and new[]/delete[].
 //
 // Example usage (scoped_ptr<T>):
@@ skipping 40 matching lines @@
 //   }
 //   scoped_ptr<Foo> PassThru(scoped_ptr<Foo> arg) {
 //     return arg.Pass();
 //   }
 //
 //   {
 //     scoped_ptr<Foo> ptr(new Foo("yay"));  // ptr manages Foo("yay").
 //     TakesOwnership(ptr.Pass());           // ptr no longer owns Foo("yay").
 //     scoped_ptr<Foo> ptr2 = CreateFoo();   // ptr2 owns the return Foo.
 //     scoped_ptr<Foo> ptr3 =                // ptr3 now owns what was in ptr2.
-//         PassThru(ptr2.Pass());            // ptr2 is correspondingly NULL.
+//         PassThru(ptr2.Pass());            // ptr2 is correspondingly nullptr.
 //   }
 //
 // Notice that if you do not call Pass() when returning from PassThru(), or
 // when invoking TakesOwnership(), the code will not compile because scopers
 // are not copyable; they only implement move semantics which require calling
 // the Pass() function to signify a destructive transfer of state. CreateFoo()
 // is different though because we are constructing a temporary on the return
 // line and thus can avoid needing to call Pass().
 //
 // Pass() properly handles upcast in initialization, i.e. you can use a
@@ skipping 110 matching lines @@
         !base::is_convertible<T*, base::subtle::RefCountedThreadSafeBase*>::
             value
   };
 };
 
 // Minimal implementation of the core logic of scoped_ptr, suitable for
 // reuse in both scoped_ptr and its specializations.
 template <class T, class D>
 class scoped_ptr_impl {
  public:
-  explicit scoped_ptr_impl(T* p) : data_(p) { }
+  explicit scoped_ptr_impl(T* p) : data_(p) {}
 
   // Initializer for deleters that have data parameters.
   scoped_ptr_impl(T* p, const D& d) : data_(p, d) {}
 
   // Templated constructor that destructively takes the value from another
   // scoped_ptr_impl.
   template <typename U, typename V>
   scoped_ptr_impl(scoped_ptr_impl<U, V>* other)
       : data_(other->release(), other->get_deleter()) {
     // We do not support move-only deleters.  We could modify our move
     // emulation to have base::subtle::move() and base::subtle::forward()
     // functions that are imperfect emulations of their C++11 equivalents,
     // but until there's a requirement, just assume deleters are copyable.
   }
 
   template <typename U, typename V>
   void TakeState(scoped_ptr_impl<U, V>* other) {
     // See comment in templated constructor above regarding lack of support
     // for move-only deleters.
     reset(other->release());
     get_deleter() = other->get_deleter();
   }
 
   ~scoped_ptr_impl() {
-    if (data_.ptr != NULL) {
+    if (data_.ptr != nullptr) {
       // Not using get_deleter() saves one function call in non-optimized
       // builds.
       static_cast<D&>(data_)(data_.ptr);
     }
   }
 
   void reset(T* p) {
     // This is a self-reset, which is no longer allowed: http://crbug.com/162971
-    if (p != NULL && p == data_.ptr)
+    if (p != nullptr && p == data_.ptr)
       abort();
 
     // Note that running data_.ptr = p can lead to undefined behavior if
     // get_deleter()(get()) deletes this. In order to prevent this, reset()
     // should update the stored pointer before deleting its old value.
     //
     // However, changing reset() to use that behavior may cause current code to
     // break in unexpected ways. If the destruction of the owned object
     // dereferences the scoped_ptr when it is destroyed by a call to reset(),
     // then it will incorrectly dispatch calls to |p| rather than the original
     // value of |data_.ptr|.
     //
-    // During the transition period, set the stored pointer to NULL while
+    // During the transition period, set the stored pointer to nullptr while
     // deleting the object. Eventually, this safety check will be removed to
     // prevent the scenario initially described from occuring and
     // http://crbug.com/176091 can be closed.
     T* old = data_.ptr;
-    data_.ptr = NULL;
-    if (old != NULL)
+    data_.ptr = nullptr;
+    if (old != nullptr)
       static_cast<D&>(data_)(old);
     data_.ptr = p;
   }
 
   T* get() const { return data_.ptr; }
 
   D& get_deleter() { return data_; }
   const D& get_deleter() const { return data_; }
 
   void swap(scoped_ptr_impl& p2) {
     // Standard swap idiom: 'using std::swap' ensures that std::swap is
     // present in the overload set, but we call swap unqualified so that
     // any more-specific overloads can be used, if available.
     using std::swap;
     swap(static_cast<D&>(data_), static_cast<D&>(p2.data_));
     swap(data_.ptr, p2.data_.ptr);
   }
 
   T* release() {
     T* old_ptr = data_.ptr;
-    data_.ptr = NULL;
+    data_.ptr = nullptr;
     return old_ptr;
   }
 
  private:
   // Needed to allow type-converting constructor.
   template <typename U, typename V> friend class scoped_ptr_impl;
 
   // Use the empty base class optimization to allow us to have a D
   // member, while avoiding any space overhead for it when D is an
   // empty class.  See e.g. http://www.cantrip.org/emptyopt.html for a good
   // discussion of this technique.
   struct Data : public D {
     explicit Data(T* ptr_in) : ptr(ptr_in) {}
     Data(T* ptr_in, const D& other) : D(other), ptr(ptr_in) {}
     T* ptr;
   };
 
   Data data_;
 
   DISALLOW_COPY_AND_ASSIGN(scoped_ptr_impl);
 };
 
 }  // namespace internal
 
 }  // namespace base
 
 // A scoped_ptr<T> is like a T*, except that the destructor of scoped_ptr<T>
 // automatically deletes the pointer it holds (if any).
 // That is, scoped_ptr<T> owns the T object that it points to.
-// Like a T*, a scoped_ptr<T> may hold either NULL or a pointer to a T object.
-// Also like T*, scoped_ptr<T> is thread-compatible, and once you
+// Like a T*, a scoped_ptr<T> may hold either nullptr or a pointer to a T
+// object. Also like T*, scoped_ptr<T> is thread-compatible, and once you
 // dereference it, you get the thread safety guarantees of T.
 //
 // The size of scoped_ptr is small. On most compilers, when using the
 // DefaultDeleter, sizeof(scoped_ptr<T>) == sizeof(T*). Custom deleters will
 // increase the size proportional to whatever state they need to have. See
 // comments inside scoped_ptr_impl<> for details.
 //
 // Current implementation targets having a strict subset of  C++11's
 // unique_ptr<> features. Known deficiencies include not supporting move-only
 // deleteres, function pointers as deleters, and deleters with reference
 // types.
 template <class T, class D = base::DefaultDeleter<T> >
 class scoped_ptr {
   MOVE_ONLY_TYPE_FOR_CPP_03(scoped_ptr, RValue)
 
   COMPILE_ASSERT(base::internal::IsNotRefCounted<T>::value,
                  T_is_refcounted_type_and_needs_scoped_refptr);
 
  public:
   // The element and deleter types.
   typedef T element_type;
   typedef D deleter_type;
 
-  // Constructor.  Defaults to initializing with NULL.
-  scoped_ptr() : impl_(NULL) { }
+  // Constructor.  Defaults to initializing with nullptr.
+  scoped_ptr() : impl_(nullptr) {}
 
   // Constructor.  Takes ownership of p.
-  explicit scoped_ptr(element_type* p) : impl_(p) { }
+  explicit scoped_ptr(element_type* p) : impl_(p) {}
 
   // Constructor.  Allows initialization of a stateful deleter.
-  scoped_ptr(element_type* p, const D& d) : impl_(p, d) { }
+  scoped_ptr(element_type* p, const D& d) : impl_(p, d) {}
+
+  // Constructor.  Allows construction from a nullptr.
+  scoped_ptr(decltype(nullptr)) : impl_(nullptr) {}
 
   // Constructor.  Allows construction from a scoped_ptr rvalue for a
   // convertible type and deleter.
   //
   // IMPLEMENTATION NOTE: C++11 unique_ptr<> keeps this constructor distinct
   // from the normal move constructor. By C++11 20.7.1.2.1.21, this constructor
   // has different post-conditions if D is a reference type. Since this
   // implementation does not support deleters with reference type,
   // we do not need a separate move constructor allowing us to avoid one
   // use of SFINAE. You only need to care about this if you modify the
   // implementation of scoped_ptr.
   template <typename U, typename V>
-  scoped_ptr(scoped_ptr<U, V> other) : impl_(&other.impl_) {
+  scoped_ptr(scoped_ptr<U, V>&& other)
+      : impl_(&other.impl_) {
     COMPILE_ASSERT(!base::is_array<U>::value, U_cannot_be_an_array);
   }
 
   // Constructor.  Move constructor for C++03 move emulation of this type.
-  scoped_ptr(RValue rvalue) : impl_(&rvalue.object->impl_) { }
+  scoped_ptr(RValue rvalue) : impl_(&rvalue.object->impl_) {}
 
   // operator=.  Allows assignment from a scoped_ptr rvalue for a convertible
   // type and deleter.
   //
   // IMPLEMENTATION NOTE: C++11 unique_ptr<> keeps this operator= distinct from
   // the normal move assignment operator. By C++11 20.7.1.2.3.4, this templated
   // form has different requirements on for move-only Deleters. Since this
   // implementation does not support move-only Deleters, we do not need a
   // separate move assignment operator allowing us to avoid one use of SFINAE.
   // You only need to care about this if you modify the implementation of
   // scoped_ptr.
   template <typename U, typename V>
-  scoped_ptr& operator=(scoped_ptr<U, V> rhs) {
+  scoped_ptr& operator=(scoped_ptr<U, V>&& rhs) {
     COMPILE_ASSERT(!base::is_array<U>::value, U_cannot_be_an_array);
     impl_.TakeState(&rhs.impl_);
     return *this;
   }
 
+  // operator=.  Allows assignment from a nullptr. Deletes the currently owned
+  // object, if any.
+  scoped_ptr& operator=(decltype(nullptr)) {
+    reset();
+    return *this;
+  }
+
   // Reset.  Deletes the currently owned object, if any.
   // Then takes ownership of a new object, if given.
-  void reset(element_type* p = NULL) { impl_.reset(p); }
+  void reset(element_type* p = nullptr) { impl_.reset(p); }
 
   // Accessors to get the owned object.
   // operator* and operator-> will assert() if there is no current object.
   element_type& operator*() const {
-    assert(impl_.get() != NULL);
+    assert(impl_.get() != nullptr);
     return *impl_.get();
   }
   element_type* operator->() const  {
-    assert(impl_.get() != NULL);
+    assert(impl_.get() != nullptr);
     return impl_.get();
   }
   element_type* get() const { return impl_.get(); }
 
   // Access to the deleter.
   deleter_type& get_deleter() { return impl_.get_deleter(); }
   const deleter_type& get_deleter() const { return impl_.get_deleter(); }
 
   // Allow scoped_ptr<element_type> to be used in boolean expressions, but not
   // implicitly convertible to a real bool (which is dangerous).
   //
   // Note that this trick is only safe when the == and != operators
   // are declared explicitly, as otherwise "scoped_ptr1 ==
   // scoped_ptr2" will compile but do the wrong thing (i.e., convert
   // to Testable and then do the comparison).
  private:
   typedef base::internal::scoped_ptr_impl<element_type, deleter_type>
       scoped_ptr::*Testable;
 
  public:
-  operator Testable() const { return impl_.get() ? &scoped_ptr::impl_ : NULL; }
+  operator Testable() const {
+    return impl_.get() ? &scoped_ptr::impl_ : nullptr;
+  }
 
   // Comparison operators.
   // These return whether two scoped_ptr refer to the same object, not just to
   // two different but equal objects.
   bool operator==(const element_type* p) const { return impl_.get() == p; }
   bool operator!=(const element_type* p) const { return impl_.get() != p; }
 
   // Swap two scoped pointers.
   void swap(scoped_ptr& p2) {
     impl_.swap(p2.impl_);
   }
 
   // Release a pointer.
-  // The return value is the current pointer held by this object.
-  // If this object holds a NULL pointer, the return value is NULL.
-  // After this operation, this object will hold a NULL pointer,
-  // and will not own the object any more.
+  // The return value is the current pointer held by this object. If this object
+  // holds a nullptr, the return value is nullptr. After this operation, this
+  // object will hold a nullptr, and will not own the object any more.
   element_type* release() WARN_UNUSED_RESULT {
     return impl_.release();
   }
 
   // C++98 doesn't support functions templates with default parameters which
   // makes it hard to write a PassAs() that understands converting the deleter
   // while preserving simple calling semantics.
   //
   // Until there is a use case for PassAs() with custom deleters, just ignore
   // the custom deleter.
@@ skipping 20 matching lines @@
 
 template <class T, class D>
 class scoped_ptr<T[], D> {
   MOVE_ONLY_TYPE_FOR_CPP_03(scoped_ptr, RValue)
 
  public:
   // The element and deleter types.
   typedef T element_type;
   typedef D deleter_type;
 
-  // Constructor.  Defaults to initializing with NULL.
-  scoped_ptr() : impl_(NULL) { }
+  // Constructor.  Defaults to initializing with nullptr.
+  scoped_ptr() : impl_(nullptr) {}
 
   // Constructor. Stores the given array. Note that the argument's type
   // must exactly match T*. In particular:
   // - it cannot be a pointer to a type derived from T, because it is
   //   inherently unsafe in the general case to access an array through a
   //   pointer whose dynamic type does not match its static type (eg., if
   //   T and the derived types had different sizes access would be
   //   incorrectly calculated). Deletion is also always undefined
   //   (C++98 [expr.delete]p3). If you're doing this, fix your code.
-  // - it cannot be NULL, because NULL is an integral expression, not a
-  //   pointer to T. Use the no-argument version instead of explicitly
-  //   passing NULL.
   // - it cannot be const-qualified differently from T per unique_ptr spec
   //   (http://cplusplus.github.com/LWG/lwg-active.html#2118). Users wanting
   //   to work around this may use implicit_cast<const T*>().
   //   However, because of the first bullet in this comment, users MUST
   //   NOT use implicit_cast<Base*>() to upcast the static type of the array.
-  explicit scoped_ptr(element_type* array) : impl_(array) { }
+  explicit scoped_ptr(element_type* array) : impl_(array) {}
+
+  // Constructor.  Allows construction from a nullptr.
+  scoped_ptr(decltype(nullptr)) : impl_(nullptr) {}
+
+  // Constructor.  Allows construction from a scoped_ptr rvalue.
+  scoped_ptr(scoped_ptr&& other) : impl_(&other.impl_) {}
 
   // Constructor.  Move constructor for C++03 move emulation of this type.
-  scoped_ptr(RValue rvalue) : impl_(&rvalue.object->impl_) { }
+  scoped_ptr(RValue rvalue) : impl_(&rvalue.object->impl_) {}
+
+  // operator=.  Allows assignment from a scoped_ptr rvalue.
+  scoped_ptr& operator=(scoped_ptr&& rhs) {
+    impl_.TakeState(&rhs.impl_);
+    return *this;
+  }
 
   // operator=.  Move operator= for C++03 move emulation of this type.
   scoped_ptr& operator=(RValue rhs) {
     impl_.TakeState(&rhs.object->impl_);
     return *this;
   }
 
+  // operator=.  Allows assignment from a nullptr. Deletes the currently owned
+  // array, if any.
+  scoped_ptr& operator=(decltype(nullptr)) {
+    reset();
+    return *this;
+  }
+
   // Reset.  Deletes the currently owned array, if any.
   // Then takes ownership of a new object, if given.
-  void reset(element_type* array = NULL) { impl_.reset(array); }
+  void reset(element_type* array = nullptr) { impl_.reset(array); }
 
   // Accessors to get the owned array.
   element_type& operator[](size_t i) const {
-    assert(impl_.get() != NULL);
+    assert(impl_.get() != nullptr);
     return impl_.get()[i];
   }
   element_type* get() const { return impl_.get(); }
 
   // Access to the deleter.
   deleter_type& get_deleter() { return impl_.get_deleter(); }
   const deleter_type& get_deleter() const { return impl_.get_deleter(); }
 
   // Allow scoped_ptr<element_type> to be used in boolean expressions, but not
   // implicitly convertible to a real bool (which is dangerous).
  private:
   typedef base::internal::scoped_ptr_impl<element_type, deleter_type>
       scoped_ptr::*Testable;
 
  public:
-  operator Testable() const { return impl_.get() ? &scoped_ptr::impl_ : NULL; }
+  operator Testable() const {
+    return impl_.get() ? &scoped_ptr::impl_ : nullptr;
+  }
 
   // Comparison operators.
   // These return whether two scoped_ptr refer to the same object, not just to
   // two different but equal objects.
   bool operator==(element_type* array) const { return impl_.get() == array; }
   bool operator!=(element_type* array) const { return impl_.get() != array; }
 
   // Swap two scoped pointers.
   void swap(scoped_ptr& p2) {
     impl_.swap(p2.impl_);
   }
 
   // Release a pointer.
-  // The return value is the current pointer held by this object.
-  // If this object holds a NULL pointer, the return value is NULL.
-  // After this operation, this object will hold a NULL pointer,
-  // and will not own the object any more.
+  // The return value is the current pointer held by this object. If this object
+  // holds a nullptr, the return value is nullptr. After this operation, this
+  // object will hold a nullptr, and will not own the object any more.
   element_type* release() WARN_UNUSED_RESULT {
     return impl_.release();
   }
 
  private:
   // Force element_type to be a complete type.
   enum { type_must_be_complete = sizeof(element_type) };
 
   // Actually hold the data.
   base::internal::scoped_ptr_impl<element_type, deleter_type> impl_;
@@ skipping 37 matching lines @@
 
 // A function to convert T* into scoped_ptr<T>
 // Doing e.g. make_scoped_ptr(new FooBarBaz<type>(arg)) is a shorter notation
 // for scoped_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg))
 template <typename T>
 scoped_ptr<T> make_scoped_ptr(T* ptr) {
   return scoped_ptr<T>(ptr);
 }
 
 #endif  // BASE_MEMORY_SCOPED_PTR_H_