// 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>):
// {
// scoped_ptr<Foo> foo(new Foo("wee"));
// } // foo goes out of scope, releasing the pointer with it.
//
// {
// scoped_ptr<Foo> foo; // No pointer managed.
// foo.reset(new Foo("wee")); // Now a pointer is managed.
// foo.reset(new Foo("wee2")); // Foo("wee") was destroyed.
// foo.reset(new Foo("wee3")); // Foo("wee2") was destroyed.
// foo->Method(); // Foo::Method() called.
// foo.get()->Method(); // Foo::Method() called.
// SomeFunc(foo.release()); // SomeFunc takes ownership, foo no longer
// // manages a pointer.
// foo.reset(new Foo("wee4")); // foo manages a pointer again.
// foo.reset(); // Foo("wee4") destroyed, foo no longer
// // manages a pointer.
// } // foo wasn't managing a pointer, so nothing was destroyed.
//
// Example usage (scoped_ptr<T[]>):
// {
// scoped_ptr<Foo[]> foo(new Foo[100]);
// foo.get()->Method(); // Foo::Method on the 0th element.
// foo[10].Method(); // Foo::Method on the 10th element.
// }
//
// These scopers also implement part of the functionality of C++11 unique_ptr
// in that they are "movable but not copyable." You can use the scopers in
// the parameter and return types of functions to signify ownership transfer
// in to and out of a function. When calling a function that has a scoper
// as the argument type, it must be called with the result of an analogous
// scoper's Pass() function or another function that generates a temporary;
// passing by copy will NOT work. Here is an example using scoped_ptr:
//
// void TakesOwnership(scoped_ptr<Foo> arg) {
// // Do something with arg
// }
// scoped_ptr<Foo> CreateFoo() {
// // No need for calling Pass() because we are constructing a temporary
// // for the return value.
// return scoped_ptr<Foo>(new Foo("new"));
// }
// 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.
// }
//
// 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
// scoped_ptr<Child> to initialize a scoped_ptr<Parent>:
//
// scoped_ptr<Foo> foo(new Foo());
// scoped_ptr<FooParent> parent(foo.Pass());
//
// PassAs<>() should be used to upcast return value in return statement:
//
// scoped_ptr<Foo> CreateFoo() {
// scoped_ptr<FooChild> result(new FooChild());
// return result.PassAs<Foo>();
// }
//
// Note that PassAs<>() is implemented only for scoped_ptr<T>, but not for
// scoped_ptr<T[]>. This is because casting array pointers may not be safe.
#ifndef BASE_MEMORY_SCOPED_PTR_H_
#define BASE_MEMORY_SCOPED_PTR_H_
// This is an implementation designed to match the anticipated future TR2
// implementation of the scoped_ptr class.
#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) {
// IMPLEMENTATION NOTE: C++11 20.7.1.1.2p2 only provides this constructor
// if 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 declare something like scoped_ptr<int[10]>.
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 is a self-reset, which is no longer allowed: http://crbug.com/162971
if (p != NULL && 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
// 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)
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;
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 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. 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 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_) {
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_) { }
// 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) {
COMPILE_ASSERT(!base::is_array<U>::value, U_cannot_be_an_array);
impl_.TakeState(&rhs.impl_);
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); }
// 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);
return *impl_.get();
}
element_type* operator->() const {
assert(impl_.get() != NULL);
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; }
// 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.
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>(Pass());
}
private:
// 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_;
// Forbidden for API compatibility with std::unique_ptr.
explicit scoped_ptr(int disallow_construction_from_null);
// 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);
explicit scoped_ptr(int disallow_construction_from_null);
// Disable reset() from any type other than element_type*, for the same
// reasons as the constructor above.
template <typename U> void reset(U* array);
void reset(int disallow_reset_from_null);
// 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 T, class D>
void swap(scoped_ptr<T, D>& p1, scoped_ptr<T, D>& p2) {
p1.swap(p2);
}
template <class T, class D>
bool operator==(T* p1, const scoped_ptr<T, D>& p2) {
return p1 == p2.get();
}
template <class T, class D>
bool operator!=(T* p1, const scoped_ptr<T, D>& p2) {
return p1 != p2.get();
}
// 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_