// _GLIBCXX_RESOLVE_LIB_DEFECTS
// DR 740 - omit specialization for array objects with a compile time length
/** Specialization of default_delete for arrays, used by `unique_ptr<T[]>`
*
* @headerfile memory
* @since C++11
*/
template <typename _Tp>
struct default_delete<_Tp[]>
{
public:
/// Default constructor
constexpr default_delete() noexcept = default;
/** @brief Converting constructor.
*
* Allows conversion from a deleter for arrays of another type, such as
* a const-qualified version of `_Tp`.
*
* Conversions from types derived from `_Tp` are not allowed because
* it is undefined to `delete[]` an array of derived types through a
* pointer to the base type.
*/
template <typename _Up,
typename = _Require<is_convertible<_Up (*)[], _Tp (*)[]>>>
_GLIBCXX23_CONSTEXPR
default_delete(const default_delete<_Up[]> &) noexcept {}
/// Calls `delete[] __ptr`
template <typename _Up>
_GLIBCXX23_CONSTEXPR
typename enable_if<is_convertible<_Up (*)[], _Tp (*)[]>::value>::type
operator()(_Up *__ptr) const
{
static_assert(sizeof(_Tp) > 0,
"can't delete pointer to incomplete type");
delete[] __ptr;
}
};
/// @cond undocumented
// Manages the pointer and deleter of a unique_ptr
template <typename _Tp, typename _Dp>
class __uniq_ptr_impl
{
template <typename _Up, typename _Ep, typename = void>
struct _Ptr
{
using type = _Up *;
};
template <typename _Up, typename _Ep>
struct
_Ptr<_Up, _Ep, __void_t<typename remove_reference<_Ep>::type::pointer>>
{
using type = typename remove_reference<_Ep>::type::pointer;
};
public:
using _DeleterConstraint = enable_if<
__and_<__not_<is_pointer<_Dp>>,
is_default_constructible<_Dp>>::value>;
using pointer = typename _Ptr<_Tp, _Dp>::type;
static_assert(!is_rvalue_reference<_Dp>::value,
"unique_ptr's deleter type must be a function object type"
" or an lvalue reference type");
__uniq_ptr_impl() = default;
_GLIBCXX23_CONSTEXPR
__uniq_ptr_impl(pointer __p) : _M_t() { _M_ptr() = __p; }
template <typename _Del>
_GLIBCXX23_CONSTEXPR
__uniq_ptr_impl(pointer __p, _Del &&__d)
: _M_t(__p, std::forward<_Del>(__d)) {}
_GLIBCXX23_CONSTEXPR
__uniq_ptr_impl(__uniq_ptr_impl &&__u) noexcept
: _M_t(std::move(__u._M_t))
{
__u._M_ptr() = nullptr;
}
_GLIBCXX23_CONSTEXPR
__uniq_ptr_impl &operator=(__uniq_ptr_impl &&__u) noexcept
{
reset(__u.release());
_M_deleter() = std::forward<_Dp>(__u._M_deleter());
return *this;
}
_GLIBCXX23_CONSTEXPR
pointer &_M_ptr() noexcept { return std::get<0>(_M_t); }
_GLIBCXX23_CONSTEXPR
pointer _M_ptr() const noexcept { return std::get<0>(_M_t); }
_GLIBCXX23_CONSTEXPR
_Dp &_M_deleter() noexcept { return std::get<1>(_M_t); }
_GLIBCXX23_CONSTEXPR
const _Dp &_M_deleter() const noexcept { return std::get<1>(_M_t); }
_GLIBCXX23_CONSTEXPR
void reset(pointer __p) noexcept
{
const pointer __old_p = _M_ptr();
_M_ptr() = __p;
if (__old_p)
_M_deleter()(__old_p);
}
_GLIBCXX23_CONSTEXPR
pointer release() noexcept
{
pointer __p = _M_ptr();
_M_ptr() = nullptr;
return __p;
}
_GLIBCXX23_CONSTEXPR
void
swap(__uniq_ptr_impl &__rhs) noexcept
{
using std::swap;
swap(this->_M_ptr(), __rhs._M_ptr());
swap(this->_M_deleter(), __rhs._M_deleter());
}
private:
tuple<pointer, _Dp> _M_t;
};
// Defines move construction + assignment as either defaulted or deleted.
template <typename _Tp, typename _Dp,
bool = is_move_constructible<_Dp>::value,
bool = is_move_assignable<_Dp>::value>
struct __uniq_ptr_data : __uniq_ptr_impl<_Tp, _Dp>
{
using __uniq_ptr_impl<_Tp, _Dp>::__uniq_ptr_impl;
__uniq_ptr_data(__uniq_ptr_data &&) = default;
__uniq_ptr_data &operator=(__uniq_ptr_data &&) = default;
};
template <typename _Tp, typename _Dp>
struct __uniq_ptr_data<_Tp, _Dp, true, false> : __uniq_ptr_impl<_Tp, _Dp>
{
using __uniq_ptr_impl<_Tp, _Dp>::__uniq_ptr_impl;
__uniq_ptr_data(__uniq_ptr_data &&) = default;
__uniq_ptr_data &operator=(__uniq_ptr_data &&) = delete;
};
template <typename _Tp, typename _Dp>
struct __uniq_ptr_data<_Tp, _Dp, false, true> : __uniq_ptr_impl<_Tp, _Dp>
{
using __uniq_ptr_impl<_Tp, _Dp>::__uniq_ptr_impl;
__uniq_ptr_data(__uniq_ptr_data &&) = delete;
__uniq_ptr_data &operator=(__uniq_ptr_data &&) = default;
};
template <typename _Tp, typename _Dp>
struct __uniq_ptr_data<_Tp, _Dp, false, false> : __uniq_ptr_impl<_Tp, _Dp>
{
using __uniq_ptr_impl<_Tp, _Dp>::__uniq_ptr_impl;
__uniq_ptr_data(__uniq_ptr_data &&) = delete;
__uniq_ptr_data &operator=(__uniq_ptr_data &&) = delete;
};
/// @endcond
// 20.7.1.2 unique_ptr for single objects.
/// A move-only smart pointer that manages unique ownership of a resource.
/// @headerfile memory
/// @since C++11
template <typename _Tp, typename _Dp = default_delete<_Tp>>
class unique_ptr
{
template <typename _Up>
using _DeleterConstraint =
typename __uniq_ptr_impl<_Tp, _Up>::_DeleterConstraint::type;
__uniq_ptr_data<_Tp, _Dp> _M_t;
public:
using pointer = typename __uniq_ptr_impl<_Tp, _Dp>::pointer;
using element_type = _Tp;
using deleter_type = _Dp;
private:
// helper template for detecting a safe conversion from another
// unique_ptr
template <typename _Up, typename _Ep>
using __safe_conversion_up = __and_<
is_convertible<typename unique_ptr<_Up, _Ep>::pointer, pointer>,
__not_<is_array<_Up>>>;
public:
// Constructors.
/// Default constructor, creates a unique_ptr that owns nothing.
template <typename _Del = _Dp, typename = _DeleterConstraint<_Del>>
constexpr unique_ptr() noexcept
: _M_t()
{
}
/** Takes ownership of a pointer.
*
* @param __p A pointer to an object of @c element_type
*
* The deleter will be value-initialized.
*/
template <typename _Del = _Dp, typename = _DeleterConstraint<_Del>>
_GLIBCXX23_CONSTEXPR explicit unique_ptr(pointer __p) noexcept
: _M_t(__p)
{
}
/** Takes ownership of a pointer.
*
* @param __p A pointer to an object of @c element_type
* @param __d A reference to a deleter.
*
* The deleter will be initialized with @p __d
*/
template <typename _Del = deleter_type,
typename = _Require<is_copy_constructible<_Del>>>
_GLIBCXX23_CONSTEXPR
unique_ptr(pointer __p, const deleter_type &__d) noexcept
: _M_t(__p, __d) {}
/** Takes ownership of a pointer.
*
* @param __p A pointer to an object of @c element_type
* @param __d An rvalue reference to a (non-reference) deleter.
*
* The deleter will be initialized with @p std::move(__d)
*/
template <typename _Del = deleter_type,
typename = _Require<is_move_constructible<_Del>>>
_GLIBCXX23_CONSTEXPR
unique_ptr(pointer __p,
__enable_if_t<!is_lvalue_reference<_Del>::value,
_Del &&>
__d) noexcept
: _M_t(__p, std::move(__d))
{
}
template <typename _Del = deleter_type,
typename _DelUnref = typename remove_reference<_Del>::type>
_GLIBCXX23_CONSTEXPR
unique_ptr(pointer,
__enable_if_t<is_lvalue_reference<_Del>::value,
_DelUnref &&>) = delete;
/// Creates a unique_ptr that owns nothing.
template <typename _Del = _Dp, typename = _DeleterConstraint<_Del>>
constexpr unique_ptr(nullptr_t) noexcept
: _M_t()
{
}
// Move constructors.
/// Move constructor.
unique_ptr(unique_ptr &&) = default;
/** @brief Converting constructor from another type
*
* Requires that the pointer owned by @p __u is convertible to the
* type of pointer owned by this object, @p __u does not own an array,
* and @p __u has a compatible deleter type.
*/
template <typename _Up, typename _Ep, typename = _Require<__safe_conversion_up<_Up, _Ep>, __conditional_t<is_reference<_Dp>::value, is_same<_Ep, _Dp>, is_convertible<_Ep, _Dp>>>>
_GLIBCXX23_CONSTEXPR
unique_ptr(unique_ptr<_Up, _Ep> &&__u) noexcept
: _M_t(__u.release(), std::forward<_Ep>(__u.get_deleter()))
{
}
#if _GLIBCXX_USE_DEPRECATED
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
/// Converting constructor from @c auto_ptr
template <typename _Up, typename = _Require<
is_convertible<_Up *, _Tp *>, is_same<_Dp, default_delete<_Tp>>>>
unique_ptr(auto_ptr<_Up> &&__u) noexcept;
#pragma GCC diagnostic pop
#endif
/// Destructor, invokes the deleter if the stored pointer is not null.
#if __cplusplus > 202002L && __cpp_constexpr_dynamic_alloc
constexpr
#endif
~unique_ptr() noexcept
{
static_assert(__is_invocable<deleter_type &, pointer>::value,
"unique_ptr's deleter must be invocable with a pointer");
auto &__ptr = _M_t._M_ptr();
if (__ptr != nullptr)
get_deleter()(std::move(__ptr));
__ptr = pointer();
}
// Assignment.
/** @brief Move assignment operator.
*
* Invokes the deleter if this object owns a pointer.
*/
unique_ptr &operator=(unique_ptr &&) = default;
/** @brief Assignment from another type.
*
* @param __u The object to transfer ownership from, which owns a
* convertible pointer to a non-array object.
*
* Invokes the deleter if this object owns a pointer.
*/
template <typename _Up, typename _Ep>
_GLIBCXX23_CONSTEXPR
typename enable_if<__and_<
__safe_conversion_up<_Up, _Ep>,
is_assignable<deleter_type &, _Ep &&>>::value,
unique_ptr &>::type
operator=(unique_ptr<_Up, _Ep> &&__u) noexcept
{
reset(__u.release());
get_deleter() = std::forward<_Ep>(__u.get_deleter());
return *this;
}
/// Reset the %unique_ptr to empty, invoking the deleter if necessary.
_GLIBCXX23_CONSTEXPR
unique_ptr &
operator=(nullptr_t) noexcept
{
reset();
return *this;
}
// Observers.
/// Dereference the stored pointer.
_GLIBCXX23_CONSTEXPR
typename add_lvalue_reference<element_type>::type
operator*() const noexcept(noexcept(*std::declval<pointer>()))
{
__glibcxx_assert(get() != pointer());
return *get();
}
/// Return the stored pointer.
_GLIBCXX23_CONSTEXPR
pointer
operator->() const noexcept
{
_GLIBCXX_DEBUG_PEDASSERT(get() != pointer());
return get();
}
/// Return the stored pointer.
_GLIBCXX23_CONSTEXPR
pointer
get() const noexcept
{
return _M_t._M_ptr();
}
/// Return a reference to the stored deleter.
_GLIBCXX23_CONSTEXPR
deleter_type &
get_deleter() noexcept
{
return _M_t._M_deleter();
}
/// Return a reference to the stored deleter.
_GLIBCXX23_CONSTEXPR
const deleter_type &
get_deleter() const noexcept
{
return _M_t._M_deleter();
}
/// Return @c true if the stored pointer is not null.
_GLIBCXX23_CONSTEXPR
explicit operator bool() const noexcept
{
return get() == pointer() ? false : true;
}
// Modifiers.
/// Release ownership of any stored pointer.
_GLIBCXX23_CONSTEXPR
pointer
release() noexcept
{
return _M_t.release();
}
/** @brief Replace the stored pointer.
*
* @param __p The new pointer to store.
*
* The deleter will be invoked if a pointer is already owned.
*/
_GLIBCXX23_CONSTEXPR
void
reset(pointer __p = pointer()) noexcept
{
static_assert(__is_invocable<deleter_type &, pointer>::value,
"unique_ptr's deleter must be invocable with a pointer");
_M_t.reset(std::move(__p));
}
/// Exchange the pointer and deleter with another object.
_GLIBCXX23_CONSTEXPR
void
swap(unique_ptr &__u) noexcept
{
static_assert(__is_swappable<_Dp>::value, "deleter must be swappable");
_M_t.swap(__u._M_t);
}
// Disable copy from lvalue.
unique_ptr(const unique_ptr &) = delete;
unique_ptr &operator=(const unique_ptr &) = delete;
};
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本文解释了在编程中什么是取消引用指针的概念。当需要访问指针指向内存中的数据或值时，即指针所指向地址的内容，这个过程称为取消引用指针。文章通过简洁明了的语言帮助读者理解这一编程基础概念。
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