Extend scoped_ptr to be closer to unique_ptr. Support custom deleters, and deleting arrays.

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 the
 // 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):
@@ skipping 77 matching lines @@
 #define BASE_MEMORY_SCOPED_PTR_H_
 
 // This is an implementation designed to match the anticipated future TR2
 // implementation of the scoped_ptr class, and its closely-related brethren,
 // scoped_array, scoped_ptr_malloc.
 
 #include <assert.h>
 #include <stddef.h>
 #include <stdlib.h>
 
+#include <algorithm>  // For std::swap().
+
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/move.h"
 #include "base/template_util.h"
 
 namespace base {
 
 namespace subtle {
 class RefCountedBase;
 class RefCountedThreadSafeBase;
 }  // namespace subtle
 
+// Function object which deletes its parameter, which must be a pointer.
+// If C is an array type, invokes 'delete[]' on the parameter; otherwise,
+// invokes 'delete'. The default deleter for scoped_ptr<T>.
+template <class T>
+struct DefaultDeleter {
+  DefaultDeleter() {}
+  template <typename U> DefaultDeleter(const DefaultDeleter<U>& other) {
+    // Spec for std::default_deleter only provies this constructor of
+    // U* is implicitly convertible to T* and U is not an array type.
+    //
+    // Correct implementation should use SFINAE to disable this
+    // constructor. However, since there are no other 1-argument constructors
+    // using a COMPILE_ASSERT() based on is_convertible<> and requiring
+    // complete types is simpler and will cause compile failures for equivalent
+    // misuses.
+    //
+    // Note, the is_convertible<U*, T*> check also ensures that U is not an
+    // array. T is guaranteed to be a non-array so any U* where U is an array
+    // cannot convert to T*.
+    enum { T_must_be_complete = sizeof(T) };
+    enum { U_must_be_complete = sizeof(U) };
+    COMPILE_ASSERT((base::is_convertible<U*, T*>::value),
+                   U_ptr_must_implicitly_convert_to_T_ptr);
+  }
+  inline void operator()(T* ptr) const {
+    enum { type_must_be_complete = sizeof(T) };
+    delete ptr;
+  }
+};
+
+// Specialization of DefaultDeleter for array types.
+template <class T>
+struct DefaultDeleter<T[]> {
+  inline void operator()(T* ptr) const {
+    enum { type_must_be_complete = sizeof(T) };
+    delete[] ptr;
+  }
+
+ private:
+  // Disable this operator for any U != T because it is undefined to execute
+  // an array delete when the static type of the array mismatches the dynamic
+  // type.
+  //
+  // References:
+  //   C++98 [expr.delete]p3
+  //   http://cplusplus.github.com/LWG/lwg-defects.html#938
+  template <typename U> void operator()(U* array) const;
+};
+
+template <class T, int n>
+struct DefaultDeleter<T[n]> {
+  // Never allow someone to delcare something like scoped_ptr<int[10]>.

[gromer, 2012/12/12 17:29:57]

Is there any particular reason to enforce this? I'm pretty sure it won't work
anyway (and in the unlikely event that it does, why not let it?)

[awong, 2012/12/12 21:00:14]

I think without this, you actually do the wrong thing.

scoped_ptr<int[10]> goes to DefaultDeleter<int[10]> which would resolve by
default to the single-object version above because it doesn't match the
specialization.

[gromer, 2012/12/14 16:57:26]

Still, it's odd that std::unique_ptr doesn't make this provision. Are you able
to demonstrate this problem in actual code?

[awong, 2012/12/14 20:25:26]

Kinda...

If I remove this code and then do:

int array[10];
scoped_ptr<int[10]> x(&array);

Clang dies with the following error:
In file included from ../../base/memory/scoped_ptr_unittest.cc:5:
../../base/memory/scoped_ptr.h:138:5: error: 'delete' applied to a
pointer-to-array type 'int *[10]' treated as delete[] [-Werror]
    delete ptr;
    ^      ~~~
          []
../../base/memory/scoped_ptr.h:215:7: note: in instantiation of member function
'base::DefaultDeleter<int [10]>::operator()' requested here
      static_cast<D&>(data_)(data_.ptr);


Also, I have been unable to actually construct a "new expression" that would
validly create a pointer-to-sized-array.  I'm starting to believe it is
impossible...but I haven't found langauge stating it definitely.

On the otherhand, this explcitly is possible

   scoped_ptr<int[10]> x(new [m][10]);

By 5.3.4.5 [expr.new]p5, the type of "new [m][10]" is int(*)[10] which would
match and then do the wrong thing if the delete call actually didn't give a
warning.

Assuming there is no way to use a single-object new expression to create an
int*[10], this feels like it might a hole in the default_deleter spec...

[gromer, 2012/12/14 21:11:46]

I'm confused; doesn't this answer your question? Isn't "new [m][10]" a new
expression that validly creates a pointer-to-sized-array?
Yeah, considering all you hit was a warning, not a mandatory diagnostic, this
looks like a hole in the standard. I'll ask on the LWG reflector, and I withdraw
my objection to this code.

[awong, 2012/12/14 21:18:39]

Yes...but it must be matched with an delete[].  Without this compile assert, we
entered undefined behavior land per [expr.delete]p2.
I am now fairly convinced that is impossible to construct a scoped_ptr<int[10]>
(or unique_ptr<int[10]>) that will "do the right thing."

Also found this:
  http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#740

which interestingly states that pointer decay would cause this to not compile
anyways, so you don't need a static_assert.  I think I disagree.

+  COMPILE_ASSERT(sizeof(T) == -1, do_not_use_array_with_size_as_type);
+};
+
+// Function object which invokes 'free' on its parameter, which must be
+// a pointer. Can be used to store malloc-allocated pointers in scoped_ptr:
+//
+// scoped_ptr<int, base::FreeDeleter> foo_ptr(
+//     static_cast<int*>(malloc(sizeof(int))));
+struct FreeDeleter {
+  inline void operator()(void* ptr) const {
+    free(ptr);
+  }
+};
+
 namespace internal {
 
 template <typename T> struct IsNotRefCounted {
   enum {
     value = !base::is_convertible<T*, base::subtle::RefCountedBase*>::value &&
         !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) { }
+
+  // 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) {
+      // Not using get_deleter() saves one function call in non-optimized
+      // builds.
+      static_cast<D&>(data_)(data_.ptr);
+    }
+  }
+
+  void reset(T* p) {
+    // This self-reset check is deprecated.
+    // this->reset(this->get()) currently works, but it is DEPRECATED, and
+    // will be removed once we verify that no one depends on it.
+    //
+    // TODO(ajwong): Change this behavior to match unique_ptr<>.
+    // http://crbug.com/162971
+    if (p != data_.ptr) {
+      if (data_.ptr != NULL) {
+        // Note that this can lead to undefined behavior and memory leaks
+        // in the unlikely but possible case that get_deleter()(get())
+        // indirectly deletes this. The fix is to reset ptr_ before deleting
+        // its old value, but first we need to clean up the code that relies
+        // on the current sequencing.
+        static_cast<D&>(data_)(data_.ptr);
+      }
+      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;
+    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
 // dereference it, you get the thread safety guarantees of T.
 //
 // The size of a scoped_ptr is small:
-// sizeof(scoped_ptr<C>) == sizeof(C*)
-template <class C>
+// sizeof(scoped_ptr<T>) == sizeof(T*)

[gromer, 2012/12/12 17:29:57]

Might want to give a little more detail here: sizeof(scoped_ptr<T,D>) ==
sizeof(T*) iff D is an empty class. Also, be aware that strictly speaking a C++
implementation is not required to provide this property; do you have tests to
enforce it?

[awong, 2012/12/12 21:00:14]

Referred people to the scoped_ptr_impl<> comment.  Also, test added...let's see
what breaks.

[gromer, 2012/12/14 16:57:26]

"size ... is small" is redundant, and it'd be good to at least slightly hedge
the claim that they're equal. How about "A scoped ptr is small; usually,
sizeof..."

[awong, 2012/12/14 20:25:26]

Hedged it by saying "on most compilers"

[gromer, 2012/12/14 21:11:46]

I feel like this still risks giving the impression that this remains true for
arbitrary deleters, which is definitely not the case.

[awong, 2012/12/15 00:19:08]

Added more details.

[gromer, 2012/12/15 00:21:40]

FWIW I would have accepted _fewer_ details, a la my "usually" suggestion, but
this is fine too.

+//
+// 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 deleteres, and deleters with reference

[Ryan Sleevi, 2012/12/12 03:37:47]

spelling nit: deleteres -> deleters

[awong, 2012/12/12 21:00:14]

Done.

+// 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<C>::value,
-                 C_is_refcounted_type_and_needs_scoped_refptr);
+  COMPILE_ASSERT(base::internal::IsNotRefCounted<T>::value,
+                 T_is_refcounted_type_and_needs_scoped_refptr);
 
  public:
-
-  // The element type
-  typedef C element_type;
+  // The element and deleter types.
+  typedef T element_type;
+  typedef D deleter_type;
 
   // Constructor.  Defaults to initializing with NULL.
-  // There is no way to create an uninitialized scoped_ptr.
-  // The input parameter must be allocated with new.
-  explicit scoped_ptr(C* p = NULL) : ptr_(p) { }
+  scoped_ptr() : impl_(NULL) { }
+
+  // Constructor.  Takes ownership of 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) { }
 
   // Constructor.  Allows construction from a scoped_ptr rvalue for a
-  // convertible type.
-  template <typename U>
-  scoped_ptr(scoped_ptr<U> other) : ptr_(other.release()) { }
+  // convertible type and deleter.
+  //
+  // Note: C++11 unique_ptr<> keeps this destructor distinct from

[gromer, 2012/12/12 17:29:57]

destructor -> constructor

[gromer, 2012/12/12 17:29:57]

I'm not sure this comment is necessary; readers who worry about this issue will
be few and far between, and this will just add clutter for the rest of them. If
you keep it, at least make it "Implementation note:" so clients know they can
ignore it.

[awong, 2012/12/12 21:00:14]

Done.

[awong, 2012/12/12 21:00:14]

I changed it to IMPLEMENTATION NOTE.  I want to keep the comment because it's
subtle enough that it would almost certainly be missed by someone casually
modifying the code.

+  // 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.
+  template <typename U, typename V>
+  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)
-      : ptr_(rvalue.object->release()) {
-  }
-
-  // Destructor.  If there is a C object, delete it.
-  // We don't need to test ptr_ == NULL because C++ does that for us.
-  ~scoped_ptr() {
-    enum { type_must_be_complete = sizeof(C) };
-    delete ptr_;
-  }
+  scoped_ptr(RValue rvalue) : impl_(&rvalue.object->impl_) { }
 
   // operator=.  Allows assignment from a scoped_ptr rvalue for a convertible
-  // type.
-  template <typename U>
-  scoped_ptr& operator=(scoped_ptr<U> rhs) {
-    reset(rhs.release());
+  // type and deleter.
+  //
+  // Note: C++11 unique_ptr<> keeps this operator= distinct from

[gromer, 2012/12/12 17:29:57]

Same here.

[awong, 2012/12/12 21:00:14]

Done.

+  // the normal move operator. By C++11 20.7.1.2.3.4, this templated form has

[gromer, 2012/12/12 17:29:57]

move -> move assignment

[awong, 2012/12/12 21:00:14]

Done.

[gromer, 2012/12/14 16:57:26]

Still need to fix line 345

[awong, 2012/12/14 20:25:26]

Done.

+  // different requirements on for move-only Deleters. Since this
+  // implementation does not support move-only Deleters, we do not need a
+  // separate move operator allowing us to avoid one use of SFINAE.
+  template <typename U, typename V>
+  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=.  Move operator= for C++03 move emulation of this type.
-  scoped_ptr& operator=(RValue rhs) {
-    swap(*rhs->object);
-    return *this;
-  }
-
-  // Reset.  Deletes the current owned object, if any.
+  // Reset.  Deletes the currently owned object, if any.
   // Then takes ownership of a new object, if given.
-  // this->reset(this->get()) works.
-  void reset(C* p = NULL) {
-    if (p != ptr_) {
-      enum { type_must_be_complete = sizeof(C) };
-      delete ptr_;
-      ptr_ = p;
-    }
-  }
+  void reset(element_type* p = NULL) { impl_.reset(p); }
 
   // Accessors to get the owned object.
   // operator* and operator-> will assert() if there is no current object.
-  C& operator*() const {
-    assert(ptr_ != NULL);
-    return *ptr_;
+  element_type& operator*() const {
+    assert(impl_.get() != NULL);
+    return *impl_.get();
   }
-  C* operator->() const  {
-    assert(ptr_ != NULL);
-    return ptr_;
+  element_type* operator->() const  {
+    assert(impl_.get() != NULL);
+    return impl_.get();
   }
-  C* get() const { return ptr_; }
+  element_type* get() const { return impl_.get(); }
 
-  // Allow scoped_ptr<C> to be used in boolean expressions, but not
+  // 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).
-  typedef C* scoped_ptr::*Testable;
-  operator Testable() const { return ptr_ ? &scoped_ptr::ptr_ : NULL; }
+ 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; }
 
   // Comparison operators.
   // These return whether two scoped_ptr refer to the same object, not just to
   // two different but equal objects.
-  bool operator==(C* p) const { return ptr_ == p; }
-  bool operator!=(C* p) const { return ptr_ != p; }
+  bool operator==(element_type* p) const { return impl_.get() == p; }
+  bool operator!=(element_type* p) const { return impl_.get() != p; }
 
   // Swap two scoped pointers.
   void swap(scoped_ptr& p2) {
-    C* tmp = ptr_;
-    ptr_ = p2.ptr_;
-    p2.ptr_ = tmp;
+    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.
-  C* release() WARN_UNUSED_RESULT {
-    C* retVal = ptr_;
-    ptr_ = NULL;
-    return retVal;
+  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.
   template <typename PassAsType>
   scoped_ptr<PassAsType> PassAs() {
-    return scoped_ptr<PassAsType>(release());
+    return scoped_ptr<PassAsType>(Pass());
   }
 
  private:
-  C* ptr_;
+  // Needed to reach into |impl_| in the constructor.
+  template <typename U, typename V> friend class scoped_ptr;
+  base::internal::scoped_ptr_impl<element_type, deleter_type> impl_;
 
-  // Forbid comparison of scoped_ptr types.  If C2 != C, it totally doesn't
-  // make sense, and if C2 == C, it still doesn't make sense because you should
-  // never have the same object owned by two different scoped_ptrs.
-  template <class C2> bool operator==(scoped_ptr<C2> const& p2) const;
-  template <class C2> bool operator!=(scoped_ptr<C2> const& p2) const;
+  // Forbid comparison of scoped_ptr types.  If U != T, it totally
+  // doesn't make sense, and if U == T, it still doesn't make sense
+  // because you should never have the same object owned by two different
+  // scoped_ptrs.
+  template <class U> bool operator==(scoped_ptr<U> const& p2) const;
+  template <class U> bool operator!=(scoped_ptr<U> const& p2) const;
+};
 
+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. 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) { }
+
+  // Constructor.  Move constructor for C++03 move emulation of this type.
+  scoped_ptr(RValue rvalue) : impl_(&rvalue.object->impl_) { }
+
+  // operator=.  Move operator= for C++03 move emulation of this type.
+  scoped_ptr& operator=(RValue rhs) {
+    impl_.TakeState(&rhs.object->impl_);
+    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); }
+
+  // Accessors to get the owned array.
+  element_type& operator[](size_t i) const {
+    assert(impl_.get() != NULL);
+    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; }
+
+  // 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.
+  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_;
+
+  // Disable initialization from any type other than element_type*, by
+  // providing a constructor that matches such an initialization, but is
+  // private and has no definition. This is disabled because it is not safe to
+  // call delete[] on an array whose static type does not match its dynamic
+  // type.
+  template <typename U>
+  explicit scoped_ptr(U* array);
+
+  // Disable reset() from any type other than element_type*, for the same
+  // reasons as the constructor above.
+  template <typename U>
+  void reset(U* array);
+
+  // Forbid comparison of scoped_ptr types.  If U != T, it totally
+  // doesn't make sense, and if U == T, it still doesn't make sense
+  // because you should never have the same object owned by two different
+  // scoped_ptrs.
+  template <class U> bool operator==(scoped_ptr<U> const& p2) const;
+  template <class U> bool operator!=(scoped_ptr<U> const& p2) const;
 };
 
 // Free functions
-template <class C>
-void swap(scoped_ptr<C>& p1, scoped_ptr<C>& p2) {
+template <class T, class D>
+void swap(scoped_ptr<T, D>& p1, scoped_ptr<T, D>& p2) {
   p1.swap(p2);
 }
 
-template <class C>
-bool operator==(C* p1, const scoped_ptr<C>& p2) {
+template <class T, class D>
+bool operator==(T* p1, const scoped_ptr<T, D>& p2) {
   return p1 == p2.get();
 }
 
-template <class C>
-bool operator!=(C* p1, const scoped_ptr<C>& p2) {
+template <class T, class D>
+bool operator!=(T* p1, const scoped_ptr<T, D>& p2) {
   return p1 != p2.get();
 }
 
+// DEPRECATED: Use scoped_ptr<C[]> instead.
+//
 // scoped_array<C> is like scoped_ptr<C>, except that the caller must allocate
 // with new [] and the destructor deletes objects with delete [].
 //
 // As with scoped_ptr<C>, a scoped_array<C> either points to an object
 // or is NULL.  A scoped_array<C> owns the object that it points to.
 // scoped_array<T> is thread-compatible, and once you index into it,
 // the returned objects have only the thread safety guarantees of T.
 //
 // Size: sizeof(scoped_array<C>) == sizeof(C*)
 template <class C>
@@ skipping 17 matching lines @@
 
   // Destructor.  If there is a C object, delete it.
   // We don't need to test ptr_ == NULL because C++ does that for us.
   ~scoped_array() {
     enum { type_must_be_complete = sizeof(C) };
     delete[] array_;
   }
 
   // operator=.  Move operator= for C++03 move emulation of this type.
   scoped_array& operator=(RValue rhs) {
-    swap(*rhs.object);
+    reset(rhs.object->release());
     return *this;
   }
 
   // Reset.  Deletes the current owned object, if any.
   // Then takes ownership of a new object, if given.
   // this->reset(this->get()) works.
   void reset(C* p = NULL) {
     if (p != array_) {
       enum { type_must_be_complete = sizeof(C) };
       delete[] array_;
@@ skipping 61 matching lines @@
 template <class C>
 bool operator==(C* p1, const scoped_array<C>& p2) {
   return p1 == p2.get();
 }
 
 template <class C>
 bool operator!=(C* p1, const scoped_array<C>& p2) {
   return p1 != p2.get();
 }
 
-// This class wraps the c library function free() in a class that can be
-// passed as a template argument to scoped_ptr_malloc below.
-class ScopedPtrMallocFree {
- public:
-  inline void operator()(void* x) const {
-    free(x);
-  }
-};
-
+// DEPRECATED: Use scoped_ptr<C, base::FreeDeleter> instead.
+//
 // scoped_ptr_malloc<> is similar to scoped_ptr<>, but it accepts a
 // second template argument, the functor used to free the object.
 
-template<class C, class FreeProc = ScopedPtrMallocFree>
+template<class C, class FreeProc = base::FreeDeleter>
 class scoped_ptr_malloc {
   MOVE_ONLY_TYPE_FOR_CPP_03(scoped_ptr_malloc, RValue)
 
  public:
 
   // The element type
   typedef C element_type;
 
   // Constructor.  Defaults to initializing with NULL.
   // There is no way to create an uninitialized scoped_ptr.
   // The input parameter must be allocated with an allocator that matches the
   // Free functor.  For the default Free functor, this is malloc, calloc, or
   // realloc.
   explicit scoped_ptr_malloc(C* p = NULL): ptr_(p) {}
 
   // Constructor.  Move constructor for C++03 move emulation of this type.
   scoped_ptr_malloc(RValue rvalue)
       : ptr_(rvalue.object->release()) {
   }
 
   // Destructor.  If there is a C object, call the Free functor.
   ~scoped_ptr_malloc() {
     reset();
   }
 
   // operator=.  Move operator= for C++03 move emulation of this type.
   scoped_ptr_malloc& operator=(RValue rhs) {
-    swap(*rhs.object);
+    reset(rhs.object->release());
     return *this;
   }
 
   // Reset.  Calls the Free functor on the current owned object, if any.
   // Then takes ownership of a new object, if given.
   // this->reset(this->get()) works.
   void reset(C* p = NULL) {
     if (ptr_ != p) {
-      FreeProc free_proc;
-      free_proc(ptr_);
+      if (ptr_ != NULL) {
+        FreeProc free_proc;
+        free_proc(ptr_);
+      }
       ptr_ = p;
     }
   }
 
   // Get the current object.
   // operator* and operator-> will cause an assert() failure if there is
   // no current object.
   C& operator*() const {
     assert(ptr_ != NULL);
     return *ptr_;
@@ skipping 71 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_